Refactored SchemaChecker

Done

When dropping the database schema, tables and sequences are only
dropped if they are present.

This commit avoids the message "table or view does not exist" by
modifying cta-catalogue-schema-drop to simply not try to delete
tables that do not exist.

cta/CTA#87 cta-catalogue-delete-all-data and cta-catalogue-schema-drop should require interactive confirmation

Removed the now redundant locking commands for the catalogue schema.
These commands were made redundant when the cta-catalogue-schema-drop
command was made interactive.

cta/CTA#87 cta-catalogue-delete-all-data and cta-catalogue-schema-drop should require interactive confirmation

Made the cta-catalogue-schema-drop command interactive

Also organised common in subdirectories, and added sub directory for mockDB.

Added the unique pointer for sqlite statements with custom deleter and fixed the error reporting for SQLite prepare

License comment is no longer filtered out by doxygen when generating web pages of the individual source files.

Created AdminUsersList in the object store as a first step to implement an object store middle tier.
Some namespace fixes for unit tests.

Implemented the new interface on the Rados backend.
Fixed several bugs.