Review the logic for the function get_all_tables

• The function get_all_tables is used to get the list of the database tables including alias tables.
• It is called by the controller plugin_dbui/dbui_conf to create the Ext JS configuration files for the client.
• The web2py scheduler introduces additional database tables which are never used by the client. However the controller plugin_dbui/dbui_conf creates the configuration files for these tables!
• In order to improve the situation, the list of tables used by the client should be tunable by adding more plugin_dbui configuration parameter like tables, excluded_tables. In addition the relation with the tables variable defined in the model common_setting.py has to be reviewed.