[578422] Extend subscriber retrieval through extension points

- Manage providers in registry and expose registry through UI plugin
- Providers can map from comparison input data to Team subscriber
- Providers may be ranked to allow for easier execution control
- Use previous subscriber retrieval behavior in new subscriber provider

Bug: 578422
Change-Id: Ifd1dc9e7d5dbc19cdd2f9c1d6899ea1049475845
Signed-off-by: Martin Fleck <mfleck@eclipsesource.com>
9 files changed