Disable ASP.NET Request Validation, make sure all output is encoded

[riipah]

VocaDB is still using the default ASP.NET request validation which prevents posting HTML or other suspicious inputs.

However, this mechanism is too limited, as many entries use characters that are currently blocked by the request validation. A better way would be to disable request validation at least for entry submissions and instead make sure that output is encoded in all cases. Output encoding should obviously be done in any case, even if request validation is still enabled.

This task includes mostly testing, making sure that cross site scripting isn't possible.