PostgreSQL: support for materialized views

Added support for materialized views with the following features:
- create (new option next to create view)
- alter
- show structure
- move to schema
- materialized views are now displayed correctly in menu and schema list
- English and Czech translation (2 new strings)

2nd commit:
- foreign tables are now displayed correctly in menu and schema list
This is not needed, the form is sent to the same page so you can use $_GET["materialized"] even after POST.