Search on Enter key.
Insert class attribute for card-specific styling
Fix timeboxing and clean up old session code
Move sync account from menu to preferences
Login preference strings and username check
Fixed version to match latest released alpha
Bumped version to 2.1alpha2
Sorting order of new cards
Options strings and limits
Deck options validation and input range limits
Don't center-align cards.
Issue 1401: Text color for white-theme buttons.

Currently the buttons do not have an explicit text color. This works if
the device default theme has a proper color for the text by default, but
fails if the default color is not readable.

This commit makes the color explicit and therefore makes it the same on
all devices.
Options group management
Reorder cards according to default group order when deleting options group.
Fix sync issue with multiple users on android 4.2 (issue 1609)
Back button on tablet congrats screen should return to overview
Set language from settings on start (Issue 1309)
Custom preferences for number range and steps input.

Also catch number format exceptions in custom study input to avoid
crashing the application.
Deck options XML formatting
Fix for Issue 1598: Filtered deck crash when revealing answer