NOTE: This patch would modify all Backend's data.
And this will cause a very long time to restart be.
So if you want to interferer your product environment,
you should upgrade backend one by one.
1. Refactoring be is to clarify the structure the codes.
2. Use unique id to indicate a rowset.
Nameing rowset with tablet_id and version will lead to
many conflicts among compaction, clone, restore.
3. Extract an rowset interface to encapsulate rowsets
with different format.
Before RowBlock will reserve memory for all columns in schema, even if
it is not queried. Which will cause bad performance when quering wide
table.
In this patch, RowBlock will reserve memory for needed columns. In a
case, this reduce ConvertBatchTime from 10s to 60ms when quering a wide
table who has 178 columns.
#1236
