[TAP] Auto-detect the RegTAP datamodel from the schemas and tables declared

in TAP_SCHEMA.

RegTAP is detected successfully if the schema 'rr' exists (case sensitive)
and contains at least the following tables (names also case sensitive):
	- capability
	- interface
	- intf_param
	- relationship
	- res_date
	- res_detail
	- res_role
	- res_schema
	- res_subject
	- res_table
	- resource
	- table_column
	- validation

The table name can be prefixed by 'rr' (case sensitive) or not. For instance:
'rr.capability' and 'capability' are both detected successfully.

All these constraints (including the case sensitive one) are based on the
requirements of the RegTAP-1.0 standard document. They are set in order
to not declare the RegTAP DM by accident AND to provide a first low
validation of the RegTAP schema and tables. Low validation because
columns (as well as datatype, utypes, indices and UDF functions) are
never checked.

This commit resolves the GitHub issue #51