* move api code to server/api
* move grpc server for agent communication to server/grpc
* move server.Config to server/config.go as it is used by both server/api and server/grpc
* move shared code used by server/api and server/grpc to server/shared
# Config resolution
- pipeline-config setting empty / not specified (default): `.woodpecker/` => `.woodpecker.yml` => `.drone.yml`
- pipeline-config setting defined by user: try that file / folder and no fallback (if a user sets some special value that is normally done for some reason)
# Changes
- pipeline-config setting will be empty by default
- remove fallback setting for config loading (simplifies config)
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closes#133
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* adjust config fetching mechanism
* default path empty
* remove fallback flag from ui and db
closes#271
- filter pipeline config folders for `.yml` and `.yaml` files
- improve `fetchConfig` tests
- update remote mock and correct wrong folder name `mock` => `mocks` to match package name
- fix: return correct filename for fallback
- improve config loading by checking if folder or not before sending api call
