Improving Hovercards' settings dialog to fulfill design specification.
Also fixing HTML structure by removing invalid `radiogroup` element and
adding missing `</div>` element, fixing related QUnit test.
Changes:
* Add close icon instead of using text
* Style header as a table for alignment
* Remove redundant "OK" button and have it replace "Save" instead
* Update text of "OK" button to "Done"
* Fix description for translation of "Done" button
* Fix qunit and selenium tests
* Remove unnecessary markup and less
* Add mediawiki-ui-button and mediawiki-ui-icon dependencies
* Shrink dialog width some per design spec
* Fix dialog horizontal position calculation to remove hard-coded value
Bug: T138612
Change-Id: I7395e3438836149becdd576942bdaf6f21b4163f
Test whether:
* "Enable previews" footer link correctly appears/disappears;
* A hovercard correctly shows/doesn't show when enabled/disabled.
Bug: T133054
Change-Id: I55f311b6b8845e6ebf4cc5698758afd1f9042a45
Basic feature of browsing a page, hovering a link, and showing/hiding
a hovercard.
Depends-On: Ie94fa399512be041f12b2f7cada20d4206ddaf82
Bug: T133019
Change-Id: Idf39e7e2a3b343babd6d0538225b4ef9002e8ac1