Merge branch '778-move-unit-tests-into-their-respective-modules' into 'master'

Move all unit tests to their modules and remove briar-tests

There are now tests in these modules:
* bramble-api
* bramble-core
* bramble-j2se
* briar-core
* briar-android

In order to run all -core tests together, the following AS run configuration can be used:
![Screenshot_2016-12-12_16-37-53](/uploads/8c706406f015ecd9e2371ebc28e6b34c/Screenshot_2016-12-12_16-37-53.png)

Closes #778

See merge request !456