Feature: Allow configuring GitLab instance without selecting a project

I have fallen for the same issue which is brought up in here: #77

I know that fetching the project-related resources only works if the plugin knows which project it maps to in GitLab. But silently ignoring the settings is somewhat unintuitive.

Solutions I would suggest, ranked from favorite to least-favorite:

1. Enable some kind of auto-detection that searches from GitLab projects matching the local project-name or repository root/remote. The Git remote might be used for that. If there is any disambiguation, a popup could ask to select one from the candidates whenever a GitLab action is performed.

2. Allow saving of GitLab instance options without an assigned project. Optionally add a warning that it will not work yet, if this is not set. But this would allow configuring it as a default-value for new projects. Whenever a GitLab action is performed, a popup warns, that this is not configured yet.

3. Warn the user when trying to save a GitLab connection without an assigned project, simply not allowing to save without setting it.

Open for input!

Solution 2 looks like the right way to go : it allows to pre-save the common settings, then all that's left to do is match the project when creating/cloning it (which could be done automatically by looking at the origin in the git config file I believe)