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
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
Update gradle, android plugin, support library,...

* Gradle (wrapper) updated from 1.11 to 1.12
* Gradle Android plugin updated from 0.9.+ to 0.11.+
* Support Library updated from 18.0.+ to 19.1.0
* Build Tools updated from 19 to 19.1.0
* NEW plugin android-sdk-manager, will download new build tools, SDK
  versions,... as declared in `build.gradle` on demand
* Checkstyle is now part of the `build` lifecycle
* `gradle.properties` file added, includes the daemon and parallel
  execution. AFAIK this is not honoured by AS as it has its own settings
  and uses the daemon by default, but it speeds up commandline builds
  (not clean builds but incremental ones). Benchmarks below.
* Had to change the classpath variable of the checkstyle task because
  otherwise it wouldn't compile for me. Works on my machine doing `gw
  checkstyle`.

Benchmarks:
Not parallel:
```
gw clean:
Total time: 13.921 secs

gw assDe:
Total time: 1 mins 32.123 secs

gw clean:
Total time: 12.841 secs

gw assDe:
Total time: 1 mins 19.26 secs

gw clean:
Total time: 13.316 secs

gw assDe:
Total time: 1 mins 26.894 secs

gw assDe:
Total time: 12.774 secs

gw assDe:
Total time: 13.149 secs
```

Parallel + Daemon
```
gw clean:
Total time: 12.18 secs

gw assDe:
Total time: 1 mins 10.839 secs

gw clean:
Total time: 4.368 secs

gw assDe:
Total time: 1 mins 27.029 secs

gw clean:
Total time: 4.055 secs

gw assDe:
Total time: 1 mins 6.845 secs

gw assDe:
Total time: 5.357 secs

gw assDe:
Total time: 3.644 secs
```

Results:
`gw clean build` is a bit faster, but not by a lot, `clean` is a
lot faster, as are subsequent incremental builds (note: not really an
incremental build in this case, because the source wasn't modified at
all). I use these settings at work on the console and did not encounter
any problems so far. For parallel builds in Android Studio, see the
compiler settings there.

Notes:
I use `gw` instead of `./gradlew` or `../gradlew` (see [this][1] post
by Jakewharton for more info) as well as [task name abbreviation][2] in
case you wonder what exactly I am doing in the benchmarks, `assDe` = `assembleDebug`.

[1]: https://plus.google.com/+JakeWharton/posts/hPkaEwza6HG
[2]: http://www.gradle.org/docs/current/userguide/userguide_single.html#N107F0

* Fix excludes for checkstyle gradle task

* Adapt to new directory layout of build/

See [this G+ post][1] (down in the comments, search for 'intermediates')
for more details.

[1]: https://plus.google.com/+AndroidDevelopers/posts/Tzof6zatrJW

* ignore new lint checks
Merge pull request #999 from Catrobat/ar/updates

Update gradle, android plugin, support library,...
z-index handle changed.  every value used only once from 1 to n.
Fix most of InflateParams, ignore others
Fix GradleOverrides
refactor Lint options

- only specific Lint ignores reside in lint.xml
- remove unused res-folders
- ignore unused drone.png file - code currently commented
- some code formatting (auto formatter)
notification icon changed to black/white
Update README.md

Adding link to new setup of the working environment