TISTUD-6674:Content Assist: Documentation link in Content assist opens invalid URL

1. Created a new extension of the com.aptana.editor.common.textHover in titanium UI to handle titanium
specific URIs
2. Handled titanium specific URIs in a subclass
3. Added new test for the same.
I'd prefer we _not_ make references to titanium project natures in studio3 codebase. Isn't there a mechanism for matching enablement expression based on how specific the variable used is? I recall Eclipse having infrastructure for that, so in this impl you'd just say always enabled and not reference any vars.