[repo view] Clean-up integration with the properties view
* Move constants to RepositoryRemotePropertySource
* Use ConfigConstants for "remote" and "url"
* Enable nested properties in RepositoryPropertySourceProvider
* Use a nested ListPropertySource for multi-valued properties
* Fix updating the view toolbar
The net user-visible result is very minor: when there are, e.g.,
multiple fetch RefSpecs, they are now shown as "[spec1, spec2]"
instead of "[spec1][spec2]", and the property is an expandable
node that shows each RefSpec on its own line when expanded.
Change-Id: Ia12ee31469f4192b5a0a3771118accc8297a4521
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>