Added hardcoded namespace constants for easy access.

The namespace model gives access to the namespaces in the database. In
the controllers (and other code), these namespaces currently referred to
using their ids (like 3 for project and 4 for graduation). This doesn't
help the readability.

So, now the ns model has 5 named constants that refer to the currently
existing namespaces: the other code can now refer to a namespace using
ns.PROJECT or ns.GRADUATION. I know this isn't very dynamic and future
proof, but so isn't the current code using the plain ids. Namespaces are
not added every week, so we're pretty safe for the moment.
Use namespace constants instead of plain ids.
Mystery commit (no changes, but git still thinks so).
Reformatted the code in upload.php (bit more understandable).

Also uses the new namespace constants (like ns::NEWS instead of the number 2).
Use the namespace constants instead of numeric ids.
Added hardcoded EN/NL constants to localization.

Also reformatted the php a bit.
WebPageController now uses the namespace and localization constants.
Removed the old structure sql script.
Fixed the 'edit page popup' preventing the unnecessary loading of preview images that don't exist.

The <img src=""> tags were filled with incomplete data because they are within templates.
Added comments to WebPage and WebPageController.
Added /gradvid/gradtest.js because it's used to enable video's.
Merge branch 'dev'
Fix unexpected php error about 'can only pass variables by reference'.
Merge branch 'dev'