move to leveldb storage

[vmakhaev]

Using leveldb on client shows race condition that should be investigated

[gritzko]

(1) the race is because of the LevelStorage.prototype.isRoot flag. Server-side storage needs "true", client-side cache needs "false".
isRoot means "this storage is the root of the replica tree".

[gritzko]

(2) Does it work without the timeout?

[vmakhaev]

1. Ok, I will test it
2. It works, but as far as it thinks that list is empty, it adds new empty item each time you clear client's storage and reload app

[vmakhaev]

isRoot did not solve the problem. Maybe problem in initialization of Vector.