add proguard config - optimizing code and delete logs
checkboxes removed after delete dialog is cancelled.
Merge pull request #984 from Catrobat/cat-853

checkboxes removed after delete dialog is cancelled.
CAT-853
fixed english translation: "Click" & "Press" --> "Tap"
fixed german translation: "Klicke" --> "Tippe"
Merge pull request #986 from Catrobat/issue#976

fixed issue #976 (localization strings)
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
fixed issue #797: handle audio focus in StageActivity
Merge pull request #975 from Catrobat/issue#797

fixed issue #797: handle audio focus in StageActivity
Added exceptions when loading projects has errors
UtilFile.java/loadExistingOrCreateStandardDroneProject updated
DroneBrickLayoutTest.java/testBricksPrototypeView updated
MainMenuActivityTest.java/testLoadProject modified
MainMenuActivityTest.java/createTestProject modified
Merge pull request #994 from Catrobat/mj7007-refactorLoadProject

fix CAT-814 with pull request issue CAT-940 : Exceptions for Loading Projects
add Gradle task for ignoring IntelliJ Settings
Merge pull request #1000 from Catrobat/gradleStuff

add Gradle task for ignoring IntelliJ Settings
Introduced ConcurrentFormulaHashMap to BrickBaseType
Introduced custom xstream converter to support porting old projects' code.xml to new structure of code.xml