Initial buggy on-demand load

 Problems:
 - going to past doesn't stop when needed
 - prepending past items loses scroll position
 - loading future restores scroll position to selected day
New Agenda version

Past already working sluggishly
WIP
Also future agenda working sluggishly
Delete old unused code
Stop UI from blocking with Future
Remove noisy debug logging
Remove unused code
No need for this to be var
Add timings for slow operations
Optimisation: do not sort

Looks like we do not strictly speaking need the sorting, and
it makes the days extraction speed up from about 100 ms to about 10.
Use already available collection
Optimise adding load results

Drops execution time from couple of seconds
to couple of hundreds of milliseconds
Optimise adding load results

Simplifies things and might make adding
results slightly faster
Further optimise model sorting

Now updateModel usually goes in less than 50 ms
Faster new id array creation

It used to take dozens of milliseconds but
now goes in less than one
Using pre-stored value is a bit faster
Format

No functional changes
Fix style

No functional changes
Add missing @tailrec
Remove noisy timing code from fast parts