[Feature] Team: Git: Allow a branch name other than master

[miurahr]

• UI: Add branch field for repo configuration
• UI: Add branch field in new team project form
• Team: Git: Tracking branch ban be other than master

Pull request type

Please check the type of change your PR introduces:

• [ ] Bug fix
• [x] Feature
• [ ] Documentation
• [ ] Build and release changes
• [ ] Other (describe below)

Which issue to be solved?

Link: https://sourceforge.net/p/omegat/feature-requests/1531/ Title: Support using arbitrary git branch name

Link: https://sourceforge.net/p/omegat/feature-requests/918/ Title: Support Git branch in Team Project

Other information

Back port the feature from the PR #174 for technology preview.