make DatabaseStorage support pagination

[gbrvalerio]

This PR adds pagination capability on the DatabaseStorage and the correct handlers on the Request class.
Also removes the Order.limit in favor of the new Pagination.limit and fix the usage of the class throughout the app.

[tananaev]

So, which databases have you tested and is the syntax an SQL standard?

[gbrvalerio]

yes, the syntax is SQL standard (OFFSET/LIMIT).

I've tested on PGSQL and H2. Yet to validate on MS SQL

[tananaev]

Please provide a link to the SQL standard with this.

And let me know once you test everything.

[gbrvalerio]

PGSQL
"For compatibility with PostgreSQL, MySQL also supports the LIMIT row_count OFFSET offset syntax." ...

the first definition appears on the SQL:2011 spec.