Lazy load room summaries from the cache

[manuroe]

This task is more complex than #4382 and #4383 because we need a smarter storage for summaries. We want to be able to do smarter queries to built different kinds of room lists.

There will be a new and dedicated room summary storage. We will use a db to be able to fetch list of rooms in different manners.

We want to kill the 572ms in this log:

[MXFileStore] Start data loading from files
[MXFileStore] Loaded room messages of 625 rooms in 828ms
[MXFileStore] Loaded rooms summaries data of 625 rooms in 572ms
[MXFileStore] Loaded rooms account data of 625 rooms in 359ms
[MXFileStore] Loaded read receipts of 625 rooms in 1035ms
[MXFileStore] Loaded 2164 MXUsers in 71ms
[MXFileStore] Loaded 2 MXGroups in 1ms
[MXBaseProfiler] Task startup - storePreload for 625 units completed in 2870.760ms
[MXFileStore] Data loaded from files in 2871ms