HDX/AV: URL generation for noav

[jteresco]

Can leave out av=noav.

[HL5195]

TLDR

Added an If statement that only adds &av="..." if an AV is selected for #557

Changes

Added an If statement checking hdx.currentAV.value != hdxNoAV.value and put the code in charge of putting "&av and hdxAV.currentAV.value in the url

Additional Info

https://courses.teresco.org/metal/h/
Has the latest version

Edited hdxcallbacks.js file