Request getter casting

[emulgeator]

Right now we are casting every request parameter to its required type in the controller (or where we are using it). This should be moved into the framework, so we can have the casting in one place.
Also we can avoid the "Array to string conversion" notices by checking these special cases.
Beside the casting we should also do some validation for character encoding, as it happens day to day that a f@!$d up browser sends invalid UTF-8 sequence which can lead to strange errors such as warning from json_encode. Please read the "Character Validation" topic here: http://webcollab.sourceforge.net/unicode.html

[emulgeator]

Another thing that it would make sense to automatically trim the request params by default