Add support for branches other than master

[osilla]

More than one user complained that they don't have master in their repos. We should support all branches that have a remote.

[anatolystansler]

App should use remote's default branch, but looks like it failing, e.g. https://github.com/CENDARI/atom

[burhanhelmy]

@anatolystansler Any update on how to solve this issue? How I can change the default branch (master) to another branch?

[VictorGarritano]

As a workaround, you can change the default branch for remote, using git remote set-head <remote> <main-branch-name>. Works like a charm

[AlexWayfer]

I'm not interested in changing default branch. I have forks, and I create branches for PRs. But Sourcerer ignores these contributions.