- Update language choose dropdown to fit more languages

Fix #2872

When use builtin SSH server with concurrent operations, there are probabilities
One connection could use the command from another connections.

Fix this by set SSH_ORIGINAL_COMMAND for each command, not set in global scope.

- add border-radius to filter list items
- use color as background of label for issue/pull view page

- update glide info

- Fix go-gogs-client#10
- Related to #809

No guarantee for compatibility with future changes

Both are possible on explore and admin panel

- Allow to delete current avatar

Use hand-written SQL to do complex query

- Remove unused config settings `[picture] service`

- Migrate: #2704 #2653
- Clone: #2701
- Mirror, Pull

Improve test cases, config settings, also show SSH config settings on admin config panel.

Config option [server] SSH_LISTEN_PORT to the port the builtin SSH server will be listen.
It can be different from SSH_PORT which is supposed to be exposed in the clone URL.
This should solve the problem when user runs Gogs inside Docker container
and still want to use builtin SSH server.