- 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.

Add AttributesInBind option in new auth source form.

When <code> is nested inside <pre>, the next end tag token would not able to be the same
as outer-most start tag. So we only check outer-most start and end tag token to be the same.

Remove the possibility of using email as user name when user actually push
through combination of email and password with HTTP.

Also refactor update action function to replcae tons of arguments with
single PushUpdateOptions struct.
And define the user who pushes code as pusher, therefore variable names shouldn't
be confusing any more.

Remote repository path is renamed but does not delete
outdated local copy which still has old repository path
as remote.

When repository contains a Slack type hook,
it changes original payload content.

This patch fixes it by using a local object to store
newly created Slack payload instead of assigning
back to the same variable.

- Update locales

path.Dir can't handle Windows case, must use filepath.Dir

- Change tooltip size from mini to tiny in profile page