os.Rename does not create parent directory automatically when not exist

This prevents user retrieve arbitrary webhook by changing URL to
access webhook from other unauthorized repositories.

Initially proposed by #2376 and fixes #3068 as well.

Add start count corrector for Repository.NumClosedIssues

- 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