Mara config changes

[jankatins]

Changes:

• Use mara-config @declare_config()
• Add flask run compatibility to still initialize the app in that case
• Two features are deprecated and can be disabled with a feature flag: registering all imported modules (use app.app.compose_app() functionality from mara_config to explicitly register functionality) and registering the click commands as subcommands of flask subcommand (use mara subcommand)
• Switch to using wsgi.py to make the flask app discovery working
• Adjust Makefile snippets to mara commands

[martin-loetzsch]

A lot of this eventually ended up in mara app