- Allow to delete current avatar

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.

- #1904 minor fix on image link

Signed-off-by: Unknwon <u@gogs.io>