Add ability to authorize gitlab account

Caveats

• Clicking Edit Power-Up Settings does not do anything #14 (closed)
• Clicking Link your Gitlab.com button does not work (We may not implement this in first iteration) #15
• There is no validation for the api endpoint and token at the moment #13 (closed)

closes #3 (closed)

assigned to @filipa

mentioned in issue #14 (closed)

mentioned in issue #15

changed the description

looking good @ClemMakesApps, just some minor things :)

assigned to @ClemMakesApps

resolved all discussions

resolved all discussions

assigned to @filipa

approved this merge request

merged

changed milestone to %1.0