Provide a more stable 'branch' command.

This somewhat addresses the problem in https://github.com/platformsh/platformsh-cli/issues/109#issuecomment-56787900

This:
 * tries to _create_ the new branch locally via Git, bailing if it's not possible, THEN creates the branch on platform.sh
 * provides `--force` to skip the local checks
 * replaces the `--no-build` option with `--build`