Support table schema change for data source

[wangzw]

Includes:

1. Add columns for table
2. Modify columns data type
3. Rename columns name
4. Delete columns
5. Rename tables

[PengLyu]

May be use ORM can solve the problems. I know sqlalchemy-migrate can implement .For example : If we want to change a column , we can get column info from maxwell ,we know which column is changed. So we can get the column model from source table model.Then copy this column model and replace the existing .