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.

snap/helpers/app.ini

@@ -0,0 +1,66 @@
+APP_NAME    = Gitea: Go Git Service
+RUN_USER    = root
+RUN_MODE    = prod
+CUSTOM_PATH = SNAP_DIR_DATA/custom
+
+[server]
+DOMAIN            = localhost
+PROTOCOL          = http
+HTTP_PORT         = 3001
+ROOT_URL          = http://localhost:3001/
+DISABLE_SSH       = false
+SSH_PORT          = 22
+STATIC_ROOT_PATH  = SNAP_DIR_DATA/static
+APP_DATA_PATH     = SNAP_DIR_COMMON/data
+SSH_ROOT          = SNAP_DIR_COMMON/ssh
+SSH_KEY_TEST_PATH = SNAP_DIR_DATA/sshkeytest
+
+[database]
+DB_TYPE  = sqlite3
+PATH     = SNAP_DIR_COMMON/gitea.db
+
+[repository]
+ROOT = SNAP_DIR_COMMON/repositories/data
+
+[repository.upload]
+ENABLED = true
+ALLOWED_TYPES = "image/jpeg|image/png"
+FILE_MAX_SIZE = 10
+MAX_FILES = 5
+TEMP_PATH = SNAP_DIR_COMMON/repositories/tmp
+
+[release.attachment]
+PATH = SNAP_DIR_COMMON/releases/attachments
+
+[smartypants]
+ENABLED = true
+
+[indexer]
+ISSUE_INDEXER_PATH = SNAP_DIR_COMMON/indexers/issues.bleve
+
+
+[mailer]
+ENABLED = false
+
+[service]
+REGISTER_EMAIL_CONFIRM = false
+ENABLE_NOTIFY_MAIL     = false
+DISABLE_REGISTRATION   = false
+ENABLE_CAPTCHA         = false
+REQUIRE_SIGNIN_VIEW    = false
+
+[picture]
+AVATAR_UPLOAD_PATH      = SNAP_DIR_COMMON/pictures/avatars
+DISABLE_GRAVATAR        = true
+ENABLE_FEDERATED_AVATAR = false
+
+[attachment]
+PATH = SNAP_DIR_COMMON/attachments
+
+[session]
+PROVIDER = memory
+
+[log]
+MODE      = file
+LEVEL     = Trace
+ROOT_PATH = SNAP_DIR_COMMON/log