Boolean parameter type

[stzr1123]

Issue ported from parent repository.

Problem

Right now, all variables are just simple Strings. It would be nice to have different types. We can start by adding a boolean variable type.

Solution

Add boolean type to the available parameter types.

The UI should render a checkbox instead of a String field. It should be possible to define the mapping from this checkbox state (e.g. checked -> true, unchecked -> false or checked -> 1, unchecked -> 0).

Take a look at the parameter types wiki to better understand this problem.

[analytically]

+1