Improve REST-API Access Control

Implement finer-grained control of REST-API users. Initial requirement is to be able to restrict the REST-API access only to the query editor.

For the SQL endpoint in particular, certain extra limits should be added:

• Add per-user result size limits or add global size limit parameter in the maxscale.cnf file

Original description:

View access only on GUI query editor for few users

Implement a feature only GUI view access for query editor tab and hide all the rest of the dashboard GUI. We want to give only query editor GUI to only specific users and rest of the dashboard (Monitoring, logs, user management and etc) tabs should be hide.