Allow user to define their own categories (topics)

[woodthom2]

Description

At present Harmony uses the categories from the Mental Health Catalogue, so that's what you get back when you call the match function.

Can we set up a mechanism for a user to train their own categories and send them to Harmony?

Rationale

Users have requested to use their own categories

[woodthom2]

Ideally Harmony would also allow you to have a hierarchy.

So you tell Harmony: these are my topics:

mental_health/anxiety
mental_health/depression
physical_health/diabetes/diabetes_type_2

etc

[woodthom2]

Added user-defined topics (Thanks @AlexNikic) - should be released in v1.0.5

The matcher now allows users to pre-define topics, which the matcher will now use to tag the questions where the word-to-topic cosine similarities of the questions are above a certain threshold.

#104