Spanish translation updates + other tweaks in English

Spanish translation updates:
 - Adds missing translations (extension-description-store info, missing strings.
 - Major proofread/editing:
   - Rewrites in order to make the texts flow more naturally in Spanish.
   - The extension name is unified back in English.
   - All English terms are either italicized or inside quotation marks following RAE's rules.
   - Likes and dislikes names have at least once the official translation from Google (I personally think they should all be changed to the official translation from Google, with the exception of the extension name).
   - Removed quite a few typos with accents.
   - Corrected a couple of discrepancies between the translated texts and the current English texts.

English text updates:
 - Fixed some words that needed uppercasing.
 - Adding a missing colon in the API page, for unification purposes.
 - Adding a missing "and" in the FAQ page.

Localization updates:
 - The unlocalizable strings in the Settings page of the extension should be localizable now.

Extensions/combined/popup.html

@@ -44,7 +44,7 @@
     </button>
     <br>
     <button style="margin-top: 0.3em" id="link_changelog" title="__MSG_linkChangelog__">
-      Change Log
+      __MSG_linkChangelog__
     </button>
   
     <br/>
@@ -102,20 +102,24 @@
     >
   </label>
   <br/>
-  <label class="switch" data-hover="Round down numbers (default YouTube behavior)">
+  <label class="switch" data-hover="__MSG_textRoundingNumbersHover__">
     <input type="checkbox" id="number_round_down"/>
     <span class="slider"/>
-    <span class="switchLabel">Show rounded down numbers</span>
+    <span class="switchLabel" title="__MSG_textRoundingNumbers__"
+    >__MSG_textRoundingNumbers__</span
+    >
   </label>
   <br/>
-  <label class="switch" data-hover="Make likes and dislikes format consistent">
+  <label class="switch" data-hover="__MSG_textConsistentFormatHover__">
     <input type="checkbox" id="number_reformat_likes"/>
     <span class="slider"/>
-    <span class="switchLabel">Re-format like numbers</span>
+    <span class="switchLabel" title="__MSG_textConsistentFormat__"
+    >__MSG_textConsistentFormat__</span
+    >
   </label>
   <br/>
   <div class="custom-select">
-    <label for="number_format">Number format:</label>
+    <label for="number_format">"__MSG_textNumberFormat__"</label>
     <select name="number_format" id="number_format">
       <option value="compactShort" id="number_format_compactShort"></option>
       <option value="compactLong" id="number_format_compactLong"></option>
@@ -124,26 +128,28 @@
   </div>
   <br/>
   <div class="custom-select">
-    <label class="switch" data-hover="Use custom colors for ratio bar.">
+    <label class="switch" data-hover="__MSG_textColorizeRatioBarHover__">
       <input type="checkbox" id="colored_bar"/>
       <span class="slider"/>
-      <span class="switchLabel">Colorize ratio bar</span>
+      <span class="switchLabel" title="__MSG_textColorizeRatioBar__"
+      >__MSG_textColorizeRatioBar__</span
+      >
     </label>
   </div>
-  <label class="switch" data-hover="Use custom colors for thumb icons.">
+  <label class="switch" data-hover="__MSG_textColorizeThumbsHover__">
     <input type="checkbox" id="colored_thumbs"/>
     <span class="slider"/>
-    <span class="switchLabel">Colorize thumbs</span>
+    <span class="switchLabel" title="__MSG_textColorizeThumbs__"
+    >__MSG_textColorizeThumbs__</span
+    >
   </label>
   <br/>
   <div class="custom-select">
-    <label for="color_theme">Color theme:</label>
+    <label for="color_theme">"__MSG_textColorTheme__"</label>
     <select name="color_theme" id="color_theme">
-      <option value="classic" id="color_theme_classic">Classic</option>
-      <option value="accessible" id="color_theme_accessible">
-        Accessible
-      </option>
-      <option value="neon" id="color_theme_neon">Neon</option>
+      <option value="classic" id="color_theme_classic">"__MSG_textColorTheme1__"</option>
+      <option value="accessible" id="color_theme_accessible">"__MSG_textColorTheme2__"</option>
+      <option value="neon" id="color_theme_neon">"__MSG_textColorTheme3__"</option>
     </select>
     <span
       id="color_theme_example_like"