Open contextmenu when tapping "When..." bricks

Tapping on a "When..." brick now opens the same contextmenu, that is opened when tapping on all other bricks.

- Tapping on a "When..." brick is now handled by the BrickAdapter (onClickListener)

- Deleted onCreateContextMenu and onContextItemSelected from ScriptFragment, since they are no longer needed

- Changed all Tests, where "When..." bricks are tested (onLongClick -> onClick)

- Changed all Tests, where a click on a "When..." brick is used to gain focus
Merge pull request #559 from Catrobat/issue#463

Issue#463