Improve the Kiwix Android app’s CI setup and increase the code coverage

This project aims to improve the existing test infrastructure (as well as write new tests), and refactoring parts of the code to improve test-ability and readability.

This is done by first making the package structure more robust by packaging the code into different sections on the basis of features. This would be crucial before trying to make the application testable.

This is followed by creation (and improvement) of local unit tests, integration tests and e2e tests, thus improving the overall Continuous Integration Process.