fix display of branch names with special characters

[isc-pbarton]

Fixes #914

[isc-pbarton]

CI failing I think because of changes in the intersystemsdc/iris-community:latest image. Fails to install TestCoverage. When I run locally on the same base image I get an error that no IPM registries are configured.

[isc-dchui]

Hm I'm not fully convinced we should necessarily support the "#" character (or spaces) in branch names. I feel like as long as we support this we're fine.

[isc-pbarton]

After discussion with @isc-dchui, we decided that just supporting pound sign is kind of arbitrary, but we want to keep the web UI simple rather than supporting everything. Plan is:

• support smaller set of branch names matching this default set
• add branch name validation when you create a new branch, both in web UI and source control menus
• exclude unsupported branch names from web UI, and show warning message if more branches exist with unsupported names. this keeps us reasonably compatible with other git clients