Add basic Android library support [obsolete]

[koral--]

AndroidPublishPlugin unit test cannot pass due to Gradle 5.3. requirement.

testDownstream task fails for me even on master:

Starting a Gradle Daemon, 1 incompatible Daemon could not be reused, use --status for details
Parallel execution is an incubating feature.
  Building version '2.2.6' (value loaded from 'version.properties' file).
  [INCUBATING] upgrade-dependency plugin is incubating and may change in any version.
  [INCUBATING] downstream-testing plugin is incubating and may change in any version.
Build cache is an incubating feature.
Using local directory build cache for build ':shipkit-root' (location = /home/koral/.gradle/caches/build-cache-1).
:shipkit-root:shipkit:compileJava NO-SOURCE
:shipkit-root:shipkit:compileGroovy FROM-CACHE
:shipkit-root:shipkit:processResources
:shipkit-root:shipkit:classes
:shipkit-root:shipkit:jar
  Building version '0.16.23' (value loaded from 'version.properties' file).
  [INCUBATING] upgrade-dependency plugin is incubating and may change in any version.

FAILURE: Build failed with an exception.

* What went wrong:
Please export 'GH_WRITE_TOKEN' variable first!
It is highly recommended to keep write token secure and store env variable 'GH_WRITE_TOKEN' with your CI configuration. Alternatively, you can configure GitHub write auth token explicitly (don't check this in to Git!):
  shipkit.gitHub.writeAuthToken = 'secret'

[mstachniuk]

When the PR is ready and merged please provide an example project with the usage of new plugin: https://github.com/mockito/shipkit-android-example

[koral--]

Superseded by #853