Both are possible on explore and admin panel

Collaborators have write access as default, and can be changed via repository
collaboration settings page to change between read, write and admin.

- Allow to delete current avatar

Use hand-written SQL to do complex query

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

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

Moving cache variable to template instead of in the struct.

Make it easier to keep track of upstream changes and bug fixes

Add AttributesInBind option in new auth source form.

Also fix that no matter who, still able to see organizations with private membership.

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.

TravisCI is too old for ed25519, so it can't be tested correctly.

The old API was using []byte, but was changed to string without running
the tests again.
It also sets the variables from the configuration to make them work.
Maybe there is a better way to do this.

This commit adds the possibibility to use either the native golang
libraries or ssh-keygen to check public keys. The check is adjusted
depending on the settings, so that only supported keys are let through.

This commit also brings back the blacklist feature, which was removed in
7ef9a05588. This allows to blacklist
algorythms or keys based on the key length. This works with the native
and the ssh-keygen way.

Because of #2179 it also includes a way to adjust the path to
ssh-keygen and the working directory for ssh-keygen. With this,
sysadmins should be able to adjust the settings in a way, that SELinux
is okay with it. In the worst case, they can switch to the native
implementation and only loose support for ed25519 keys at the moment.
There are some other places which need adjustment to utilize the
parameters and the native implementation, but this sets the ground work.

Was using the wrong method and now uses the method which checks if
the avatar link is relative or not.