[api] obsolete configuration in /architectures api, moving it to /distributions list

This drops "available" and "recommended" attributes in /architectures controller
to avoid conflicts.
The values get moved to /distributions and /configurations.
/architectures is read only now, because modification of architectures does anyway
need code changes in OBS.
[webui] fix broken webui architecture configuration

- all existing architectures are shown now
- set check box based on available scheduler configuration
[api] cache the project list output

susestudio's autocomplete code hammers on /build
[api] add the possibility to subscribe to events

You can subscribe globally or on project/package leel if you want to
get notifications (not yet implemented obviously) for events either for

 - none (overwriting more global defaults)
 - project maintainership
 - package maintainership
 - all