Cleanup ux branch

Take care of bugs in https://github.com/mozilla-b2g/gaia/pull/8164, https://github.com/mozilla-b2g/gaia/pull/8671


* [\#815653](https://bugzilla.mozilla.org/show_bug.cgi?id=815653) - [Settings] - remove :active for explanation items
* [\#816067](https://bugzilla.mozilla.org/show_bug.cgi?id=816067) - [FTU. UX VD] Change background.
* [\#823414](https://bugzilla.mozilla.org/show_bug.cgi?id=823414) - B2G browser gradient value does not match the gradient found in Settings
* [\#828908](https://bugzilla.mozilla.org/show_bug.cgi?id=828908) - [Settings] Hints should not be treated as list items
* [\#830111](https://bugzilla.mozilla.org/show_bug.cgi?id=830111) - [Settings] - arrange Phone lock screen
* [\#834446](https://bugzilla.mozilla.org/show_bug.cgi?id=834446) - [Browser] Truncated Bookmark Label
* [\#822585](https://bugzilla.mozilla.org/show_bug.cgi?id=822585) - [FTU UX VD] Change final illustration of the hand
* [\#827804](https://bugzilla.mozilla.org/show_bug.cgi?id=827804) - [Lockscreen UX] Entering passcode. "Emergency call" and "Cancel" buttons should be vertically centered
* [\#823793](https://bugzilla.mozilla.org/show_bug.cgi?id=823793) - [B2G][Browser]: Long site names and addresses in the Top Sites/Bookmark/History tabs do not have their text truncated gracefully
* [\#829023](https://bugzilla.mozilla.org/show_bug.cgi?id=829023) - [Settings] Don't use dividers to separate paragraphs in the same text block
* [\#835774](https://bugzilla.mozilla.org/show_bug.cgi?id=835774) - [Building Blocks] [Filters] Left border should be removed
* [\#830380](https://bugzilla.mozilla.org/show_bug.cgi?id=830380) - [FTU UX VD] Tutorial. Replace the third image
* [\#828890](https://bugzilla.mozilla.org/show_bug.cgi?id=828890) - [Settings] Scroll bar should not go over the header