WL#1317: MySQL Admin - Catalogs - Table functions

Tasks:
Complete functions to get/set/add tables

Functions:
- MYX_TABLE myx_schema_get_table(char *tablename) 

- myx_schema_add_table(MYX_TABLE table) 
  Add a new table to the schema 

- myx_schema_modify_table(MYX_TABLE table, MYX_TABLE original_table) 
  Alters an existing table