Enable activities to be joined from within the app

[kazlauskis]

At the moment, users have to join activities on the website. This would allow them to join an activity (while online) and use this activity for recording (inc. offline). This could look like what we've done for the ButterflyCount app:

[kazlauskis]

Implement an infinite scroll feature for the activities list, ensuring that the items are sorted alphabetically and include a search functionality.

[kazlauskis]

@kitenetter Currently, we ask users to select the "iRecord App data entry" as a form when setting up app activities (see here). The new activities functionality that I am porting from the ButterflyCount app uses a standard warehouse REST endpoint which John has recently set up but which doesn't have the option to filter activities based on forms. Do you want me to drop this restriction and allow users to see all the possible activities, OR should we ask @johnvanbreda to help us improve the warehouse endpoint?

There are plans to enable activities for the Plant survey, too. If we remove the "form restriction", then we are pretty much allowing any survey to send data to any activity. On the other hand, if we want to keep it the way it currently works in the app, then we should allow the app to fetch and filter the activities that have the correct form attached, not just the "iRecord App data entry".

[kazlauskis]

@kitenetter, I have implemented the new activities functionality, which allows to choose any activity for any survey (see the above comment). Are you OK with this?