Fix issue#485

Inserted notification dialog for community button.
Merge branch 'master' into issue#485
Refactor singletons
Merge pull request #527 from Catrobat/refactorSingeltons

Refactor all Singletons
Merge branch 'master' into issue#485
Detect wrong assert messages with empty string or with delta value
Merge pull request #503 from Catrobat/FixAssertionErrorMessageTest

Detect wrong assert messages with empty string or with delta value.
Merge pull request #528 from Catrobat/issue#485

Issue#485
Merge branch 'master' into LiveWallpaper_Master
LWP only - no Pocket Code. Needed for debugging purposes.