Paginate sessions

[BoD]

Loads the sessions by pages of 10, instead of loading the whole list immediately.

This is meant to look at how the Apollo Kotlin pagination system can be implemented in a real project.

Caveat: the pages are based on the contents of the list: when getting the first few items, we only know about Day 1, and only when scrolling to the end of Day 1 do we know that there's a Day 2, and the pager gets updated. Because of this, this can't be merged and I'll close the PR right now - at least it's a reference at how to use the pagination system that will be in the PR history.

The steps were:

1. depend on the incubating artifacts
2. update extra.graphqls
   2.1 mark sessions as embedded
   2.2 mark sessions.first and .after as pagination args
   2.3 mark pageInfo as embedded
3. implement a MetaDataGenerator to keep track of endCursor and after
4. implement a FieldMerger to merge the nodes lists
5. watch the sessions, so the UI is refreshed when a page is appended
6. add a fetchNextSessionsPage fun and call it from the UI when reaching the end of the LazyColumn

Note: steps 2-4 would have been simpler if the schema were following the Relay pagination spec - the rest would have been the same.

pagination.webm