Fixes:
* Sanitize user-provided content in HTML (Fixes#2193)
* Fix encoding of search query in prev/next pages (Fixes#2229)
* Fix some issues introduced with #2196:
- Fix alignment of all <h3> elements (Move the inline style from the parent to the <h3> element)
- Add missing comma on 'dir' HTML attribute (Typo introduced by PR #2196)
Code cleaning:
* Remove unnecessary 'each_sclice' + 'each' double loop in ECR files
* Clean the player's <source> list generation code (in player.ecr)
The behavior was as follow: on Right-To-Left text (e.g Arabic) that is wrapped
(because it's too long to fit on one line), the second row and following rows
may or may not be right aligned (as RTL text should be). Opening the devtools
fixes that alignement, as consistently as closing the devtool breaks it.
This problem seems to arrive only in the following configurations (link nested
in a paragraph, both of which may or may not have the dir= attribute):
* `<p><a href="some_link">RTL_TEXT</a></p>`
* `<p><a href="some_link" dir="auto">RTL_TEXT</a></p>`
* `<p dir="auto"><a href="some_link">RTL_TEXT</a></p>`
with the following CSS:
```
p {
unicode-bidi: plaintext;
text-align: start;
}
```
Changing the HTML to the following configuration (a paragraph with the dir=
attribute, nested in a link) seems to fix it:
`<a href="some_link"><p dir="auto">RTL_TEXT</p></a>`
This will prevent, on large pages, the LTR and RTL text to be
far away, on each side of the page. This could happen on channel
and playlists descriptions, when the page is displayed on a large
screen.
* Remove percent-encoding of the search query when calling youtube API, as it
breaks UTF-8
* Empty search redirects to /search, not /
* Show the fullscreen search "home page" (from #1977) at /search
* Allow 'region=' parameter to be passed to /search
* Other minor fixes
