Add merge request properties

[uhafner]

There are also several properties available for merge requests (or approvals)), but I don't find the API page. I will update this issue once I find the corresponding API page.

In my courses I need to alter the settings for

• merge method
• squash commits
• merge checks

Here is the dialog:

[obcode]

merge methods already implemented in #50

[obcode]

@uhafner:

Everything, except Title must match required pattern is implemented now.

If you do not need this feature, please close this issue. Thank you!