Allow URL customisation and specifying subset of CRUD roles.

[carltongibson]

Route only some roles:

BookmarkView.get_urls(roles={Role.LIST, Role.DETAIL})

Plus, specify url_base, and path_converter for URL routing.

Fixes #11 Fixes #32

cc. @kasun @joshuadavidthomas @jefftriplett

[jefftriplett]

Nicely done. It'll be nice to delete some class overrides and possibly templates that were mostly serving to override the action values/links. 🎉

[carltongibson]

@jefftriplett @joshuadavidthomas still has a few open issues about the actions list… #39, #40, #41 — so it might not clear up the template, just yet.

Main points are:

• Subset of methods easier.
• Customise URL, and things like UUID lookups.