Low level building blocks to read mutation transactions
MysqlStorage iterator to read records from all tables grouped by timestamp
Extracted group cache loading in a separate method
Proper generated sql comment
Fix cache loading refactoring
Test mutation group iterator error
Renamed RecordIndex to TransactionSummaryRecord
Transaction summary records load threshold not hard coded anymore
Improvements sugested by Alex
Merge pull request #87 from wajam/manu-store-read-records

MysqlStorage iterator to read records from all tables grouped by timestamp