Changed debug build variant config to allow installation of debug version alongside release variant

[alfonso133]

By adding an applicationIdSuffix in the config for debug build variant it is appended to the application package name allowing it to be installed as a separate application from the release version. In this way it is possible to debug during development (even using a separate test server) without impacting the release version (connected to the regular server for everyday use)

[alfonso133]

I don't know where to ask so I'll ask here: I noticed there are various style/convention/best practice warnings for the project as notified by sonarlint (for example: modifiers in non conventional order, implicit noargs constructor for utilities with only static methods, maps declared as hashmap instead of map, etc). I could clean up the bulk of them (in the least invasive way), would you be interested in this kind of pull request?

[dominiczedler]

Thanks, this was indeed a great idea! I just had to change the static id of a file provider, which is dynamic now. Perhaps I can add a badge on the overview page in our app if it's a debug build. And in a later version we can edit the launcher icon for this build variant (@patzly).

Thanks for your offer to correct the linter warnings, I think I can firstly look over the linter myself and then you can also correct valid warnings. With Android Studio linter I can also see many warnings:

You're always welcome to open an issue after I corrected the warnings on my side, I will write you here when I've finished it. Thanks for your interest!