New Feature Config

[tobiasrohloff]

A pretty large refactoring, but most changes are very small and easy. Instead of having different flavor-specific feature configs in Config and FeatureConfig this PR replaces these with resource-based feature flippers. The defaults can be found in /app/src/main/res/values/features.xml, which every flavor can overwrite. We allow features to be directly enabled by providing the corresponding data if required (strings and string-arrays), but also simple flags as bools. If a feature is enabled can be checked with Feature.enabled("channels") for example, no matter if this is a string, string-array or bool resource.

This should help to keep the code-base much cleaner in the long-term since more and more flavors are in the pipeline. Flavors can be added/removed without touching main at all now. Everything is encapsulated in their flavor-specific source folders.

Additional stuff:

• Apply whitelisted language config with resConfigs for each flavor app/build.gradle.
• Get rid of BuildType. Config still provides the DEBUG and RELEASE flags.
• Get rid of BuildFlavor. No flavor-specific code anymore. Everything is mapped to feature flippers.
• Other features that are not flavor- but hardware-/software-specific are still configured as fields in Feature, e.g., HLS_VIDEO and PIP.
• Provide some convenient ResourcesExtensions for easier resource fetching, also from Contexts.
• Cleanup string resources, e.g., remove unused, add missing translations, etc.

[tobiasrohloff]

@bengelhaupt @SanJSp I have to merge this since it blocks other emergency tasks. Feel free to review anyway, I'm happy to implement feedback also at a later point.

[bengelhaupt]

LGTM