phases: add a phase and phasestr method to file context

bookmarks: simplify code Remove some unnecessary return statements and collect some checks into one place. As requested by Thomas Arendsen Hein <thomas@intevation.de>.

bookmarks: abort when incompatible options are used (issue3663) Options like --delete and --rename are incompatible with each other. In this case we abort. We do not abort if the result is a nullop. Nullops are: '--delete --inactive', '--delete --force'.