refactor BrickEditFormulaTest

- extend BaseActivityInstrumentationTestCase
- adapt setup, delete unnecessary teardown
- remove member (Java warning: unused)
- fix typo
add @Device annotation

test seems to fail on emulator.
as a quickfix @Device is added
Merge pull request #549 from Catrobat/fixBrickEditFormulaTest

refactoring of BrickEditFormulaTest