add proguard config - optimizing code and delete logs
fix DRONE-15

deactivate Drone with Feature flag
improve Gradle build Feature output
add LegoNXT build flag
fix typos
Merge pull request #989 from Catrobat/DRONE-15_drone_buildflag

DRONE-15 - buildflag
Merge pull request #811 from Catrobat/proguardConfig

add ProGuard config for Optimization and removing Logs
fixes CAT-970 and CAT-654
correct messages from server are shown
Merge pull request #965 from Catrobat/errorCodes#654

Better error messages
Added exceptions when loading projects has errors
UtilFile.java/loadExistingOrCreateStandardDroneProject updated
DroneBrickLayoutTest.java/testBricksPrototypeView updated
MainMenuActivityTest.java/testLoadProject modified
MainMenuActivityTest.java/createTestProject modified