#1 Checking for the right input

[Mathias Palm]

Check for all entries for the right input and take
appropriate action if input is wrong. Example

- Check that the value for the variables are always
numbers.

This has to be done for

- value of variables type DATE
- Is the value part of the available altenatives in
variables type ENUM?
- Value of Variables type INT
- Syntactical correctness of expression strings in the
explorer