COFC zoom polish

* Zoomtilt uses camera Y alone, rather than distance from ground at zoom target. Panning, MMB, and clicking on minimap now adjust zoomtilt angle to maintain consistency.
* Zoom out to center bounds loosened slightly. Map now takes up 2/3 of the screen at full zoomout, rather than 3/4.
* maxDistY better respected as the actual camera Y limit when freemode is off. Panning and zooming out from screen center didn't previously respect this properly.
* Centering to cursor target from full zoomout with zoomtilt on improved for targets above map minimum height. Also now works off trig computations rather than hardcoded hacks.