feat(Parameters): Add boolean element type

[Hipska]

Base information

Question	Answer
Related to a SourceForge thread / Another PR / Combodo ticket?	N/A
Type of change?	Enhancement

Objective

Add enhanced support for boolean parameters which can now contain 1, 0, true, false, on, off, yes, no and return the boolean representation to the collector.

Proposed solution

Use integrated FILTER_VALIDATE_BOOL.

No Unit test added, since there's no existing test for the modified method.

Checklist before requesting a review

• I have performed a self-review of my code, and that it's compliant with Combodo's guidelines
• I have tested all changes I made on an iTop instance
• I have added a unit test, otherwise I have explained why I couldn't
• I have made sure the PR is clear and detailled enough so anyone can understand the real purpose without digging in the code