Change pipeline config path resolution (#299)

# 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)

---
closes #133

---

* adjust config fetching mechanism

* default path empty

* remove fallback flag from ui and db

store/datastore/sql/postgres/files/repos.sql

@@ -30,7 +30,6 @@ SELECT
 ,repo_gated
 ,repo_visibility
 ,repo_counter
-,repo_fallback
 FROM repos
 INNER JOIN perms ON perms.perm_repo_id = repos.repo_id
 WHERE perms.perm_user_id = $1
@@ -61,8 +60,7 @@ INSERT INTO repos (
 ,repo_gated
 ,repo_visibility
 ,repo_counter
-,repo_fallback
-) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20,$21,$22,$23)
+) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20,$21,$22)
 ON CONFLICT (repo_full_name) DO NOTHING
 
 -- name: repo-delete