This reverts commit 763cbf8493c610dec0e7e344bee40ad331e7a272.
This reverts commit ddad699b259bafe6c7ed630e7afc2eb38b7825e6.
This is causing way too many problems -
On Android with GitHub we occasionally get a User Cancelled exception.
On iOS this doesn't work < ios11
I prefer keeping my way till then. Even though it doesn't support
KeepAlive on Android.
This works slightly better on iOS and on Android it has a keep alive,
which will prevent our app from being killed. Additionally, this way
there is less for me to maintain, which is always nicer.
The API for flutter_web_auth is also much simpler.
This also inolves some custom logic for parsing the Query Parameters
from the GitLab callback, as it doesn't seem to be a proper URI. Not
sure what is going on with Gitlab.
