Better validation of branch name when creating a new branch

[isc-pbarton]

Use the "Create a new branch" option in the source control menu to create a new branch "not a valid branch name". It will fail to create a new branch because the name includes spaces, but the only indication is an error message in the source control output. We should have a more visible warning that the branch name is invalid. This might require adding a new "create new branch" page like the "Sync" page.