Instead of 2/3 which is not optimal for 512 px avatars usually passed to Core, use the sequence 7/8,
6/8, 11/16, 10/16... to do "smaller" downscaling steps and reduce aliasing effects.
Before, it was discussed that just 3/4 can be used. However:
- If we repeat the downscaling step, we get `3 ** n` as a numerator and this way increase aliasing
effects on each step. The same for 7/8. Better limit the numerator value.
- As we do downscaling in a loop only for avatars which aren't changed frequently, let's do
"smaller" steps and start from 7/8.
