StEP-366: Add OAuth2 support to Stud.IP

.gitignore

app/controllers/admin/oauth2.php

app/controllers/api/oauth2/applications.php

app/controllers/api/oauth2/authorize.php

app/controllers/api/oauth2/clients.php

app/controllers/api/oauth2/oauth2_controller.php

app/controllers/api/oauth2/token.php

app/views/admin/oauth2/_clients.php

app/views/admin/oauth2/_notices.php

app/views/admin/oauth2/_setup.php

app/views/admin/oauth2/_setup_key.php

app/views/admin/oauth2/index.php

app/views/api/oauth/authorize.php

app/views/api/oauth2/applications/details.php

app/views/api/oauth2/applications/index.php

app/views/api/oauth2/authorize.php

app/views/api/oauth2/clients/add.php

cli/Commands/OAuth2/Keys.php

cli/Commands/OAuth2/Purge.php

cli/studip