Port ConVars to transitional syntax.

I broke this up into separate commits, as much good as that'll do. I made some changes over the existing methodmap for ConVar: it uses getters/setters for its values now, and I removed the constructor due to the constructor-should-return-new-object rule. The property names are debatable.

As usual the existing plugins have been modified to use the new API. If I saw old-style decls in surrounding code I fixed those places up. Near the end of all this I'll probably run a script to convert all the remaining decls in the base plugins and .incs.