Extend Server Users

[lvca]

Right now the server users can be profiled only with which database they can access. It would be nice including also the following permissions:

1. read-only or read-write access
2. CRUD (Create/Read/Update/Delete) access per type
3. quota:
   4.1. max query per minute
   4.2. max returned records. if a query returns more records than the configured quota, they are simply discarded. This means adding an implicit limit to all the queries.

Note: this setting will be still stored in the config/security.json file because they work at the server level only.