snap-packaging for gitea (#2568)

* Modify tbraeutigam/gogs-snap for gitea

* Fix building on 16.04 (manually build go-bindata).
-> add _source.tar.bz2 to .gitignore (used by snapcraft cleanbuild)

* Streamline Snap packaging:
 - Take advantage of install-hooks (snapd 2.27)
 - Use snapctl configuration storage for unchanging values

* Move to using Snap Hooks for configuration

* Missed re-adding daemon statement

* Fix two warnings from Codacy.

.gitignore

@@ -59,3 +59,13 @@ coverage.all
 /integrations/mysql.ini
 /integrations/pgsql.ini
 /node_modules
+
+
+# Snapcraft
+snap/.snapcraft/
+parts/
+stage/
+prime/
+*.snap
+*.snap-build
+*_source.tar.bz2