Make MSA update not all data from db on modification but modified region only

Currently the msa modification process occurs the following way:
1) GUI detects modification -> 2) GUI addresses to the shared msa object ->
3) msa object modifies msa entity in database (typically that entity is altered partially) -> 4) msa object downloads all the msa entity from db -> 5) msa object emit signal to GUI for update with downloaded msa

The described scheme makes performance to suffer on the 4th step where huge alignment might be downloaded from database regardless of the actual modifications. Partial update from db would be rather cheaper in this case.

So the task is to allow partial msa update from db on modifications.