Merge tag '0.28.0' into develop

* Enhancements
  * Several content enhancements
  * [#110] Upgrade to API 20
  * [#360] Switch to grammar v3.1 allowing optional progress header
  * [#365] Pre-load sequences to avoid waiting for BK tree load in autoList questions
* Bug fixes
  * [#301, #302, #303] Design and icon fixes; also better space usage when sequences have no intro
Add missing motherTongue field in ProfileData
Bump build tools version
Reshape results layout a little
Only show the WebView once loaded

Trying to prevent the flicker of the WebView when it's shown, but I
still get a white flicker the instant the view goes from invisible to
visible.
Bump version
Update grammar versions
Update changelog
Merge branch 'release/0.29.0'