update url(...) to path(...) with 2.x style parameter capture where possible

[Pomax]

See https://docs.djangoproject.com/en/3.0/releases/2.0/#simplified-url-routing-syntax

Based on #575, we can now update url(...) patterns to path(...) patterns with much cleaner capture group syntax, and that'd be a nice thing to do.

[bheasman]

Moving to next sprint. NB - this is part of wider Django issue we need to address