Add support for iRecord Activities

[kazlauskis]

Show a list of Activities the user can join/leave from the app. The activities would be set up on the iRecord website.

Show only activities that are Lepidoptera or multi-taxa.

Surveys we should enable this feature:

• Single species
• Species list
• (skip) Single species timed count
• (skip) 15-min species count

Make the list of Activities ordered by relevance to that account; add a filter and/or search.

[kazlauskis]

@DavidRoy I am ready to work on this task, but to filter activities by species group, John or someone else will need to update this REST API endpoint to return informal species groups and accept filters.

This is also linked to #290.

[DavidRoy]

@johnvanbreda can you take this on please