Reimplementation of slug generation

Slug generation, previously implemented via JS code is now replaced with C# service

1. Ajax call to c# code
2. Slug generation based on modified code used on Stack Overflow
3. Slug verification implemented according to RFC standard
4. Unit tests added
5. Several slugs that were fatal to N2 are no longer possible (like "a b" or "a%20b")
6. It is now possible to implement replacement service for any custom implementation that might be needed