Capture -> Categorisation flow

A lot of this is captured in #235, but in the interest of keeping that issue focussed on categorisation, I wanted to open a separate issue for the user _flow_ from capture #234 to categorisation #235.

## Tasks
+ [ ] Review options and determine how separate or closely-knit we want to make the two steps (do we want to give people the option of doing them within the same flow or keep them separate to encourage the 'brain dump' facility?)
+ [ ] Create flow diagrams to illustrate flows (this may bleed into related issues)
+ [ ] Open and update any issues required (such as #235 and #234) with UI