Suppress the error when we're removing a file that may not exist

* Added rel="noopener" to target="_blank" hrefs

* Replaced gogs.io/docs with docs.gitea.io

* golint fixed for modules/setting

* typo fixed and renamed UNIXSOCKET to UnixSocket

* Lint models/release.go

* Lint models/ issue_label, issue_mail & mail.go

This was done semi-programmatically, not really documenting anything

Semi-automatic linting (don't really document things)

* Handle user ssh key input better

ssh_key: when user submitted keys had a newline at the end, strings.Split
would have created a slice with an empty last element, and the key type
check would be incorrect. Perhaps a better way is to look for 'ssh-rsa' or
'ssh-dsa' at the beginning of the string, but this is simple.

* ssh_key: correct indentation