Update database
Fix element categories
Do not export AboutActivity

This commit fixes potential fragment injection vulnerability.
Fix invalid AboutActivity's parent activity name
Add xxhdpi drawable for ic_action_search
Update drawables for ic_action_search
Add missing contentDescription to ImageView in properties_list_item layout
Add RTL support
Bump target SDK version to version 20
RTL: Do not change text direction
AboutActivity: Improve version detection
Update drawables for ic_action_wikipedia
Update database
build_db.py: Fix parsing of superscripts in articles
Update database
Use static version of gradle plugin
Update build tools version
ZoomableScrollView: Do not use initializeScrollbars()

initializeScrollbars() is deprecated in API 21.
Bump target SDK version

Use API 21 (Android 5.0) as target API.
Use Gson 2.3