closes#11
Added support:
1. Environment variable `WOODPECKER_DELETE_MULTIPLE_RUNS_ON_EVENTS` (Default pull_request, push)
2. Builds will be marked as killed when they "override" another build
* UI: let remove be a remove
* UI: add deactivate repo btn
* Store: DeleteRepo also delete related
* Store: more test coverage
Co-authored-by: 6543 <6543@obermui.de>