Move travis to docker

[StefMa]

Based on #115

• Do two build environments: unit and instrumentation (run in parallel)
• Moved unit test to docker (because of the andoird images you can't really start a emulator in docker)

Benefits of using docker:

• The docker image contains only the "sdkamanger". The sdkmanager install every build-tools or android images if they needed automatically. We don't need to update the travis.yml anymore \o\
• We can trust the docker. If the underlined host (travis <-> trusty, zenty) changed, everything just works as before. As long as we can run docker in that environment.

Benefits of the new travisscript:

• It parses automatically the BUILD_TOOLS_VERSION and the SDK_VERSION from the build.gradle file and put it into the the travis android components. We don't need to update the travis.yml anymore /o/

Do we have speed benefits?

• Unfortunately not really. Because travis is very slow with starting a emulator and stuff it won't decrease the build time. Maybe 10 seconds or so because travis don't run the unit tests anymore :)

What do test:

• If codecov works as aspected -> Checked ✅ works

[StefMa]

Seems that UnitTests are working now in docker 👍 That is great... Moving now InstrumentationTests back to travis...

[StefMa]

Read also that: https://docs.travis-ci.com/user/speeding-up-the-build/

Thinking about to have two parallel builds:

1. Native for Instrumentation Tests
2. Docker for Junit, codecov etc.

[StefMa]

\o/ 💛 :awesome: :sweet: 🍬

Here is a 🌮

[StefMa]

Next step is to cache the dependencies https://docs.travis-ci.com/user/caching/

And other 🍬 :

• Read the android components from a file instead of having it directly in the travis.yml. Maybe we can read the build-tools and sdkVersion from the build.gradle somehow 🤔

[StefMa]

Don't cache. Because we can't really delete the cache ... Make no sense with that mechanism...

[StefMa]

🤦‍♂️

[StefMa]

Currently build-tools got not parsed correctly..

[StefMa]

Rebased all. Works now 👊

Problem was that \' is valid on "mac sed" but not on "gnu sed". Replaced it with just '. Works on both sed versions...

[StefMa]

If codecov works as aspected

Seems that codecov is reporting fine \o/ See https://codecov.io/gh/grandcentrix/ThirtyInch/compare/7533ea03c848ab39911356fe2965e51070094d7e...5c2ba57fdf35738b40d97bff013b9565fdb2625e