small clarification in tag text
Scheduler improvements

Order of scheduled cards is now stable within lifetime of an actor (15 mins).
It solves 2 problems:
1) New card scheduler should be able to meaningfully enforce limits on tags. Right now it can while using some caching inside.
Also there is a high level cache for a full sequence of cards.
2) And that solves a problem of card sequence ordering on android. Now because we generate sequence id for an each card for learning.