First-person view, tracking third-person view

[Sebelino]

I added support for toggling between a first-person camera view and a tracking third-person view, in addition to the default top-down view, by pressing C. Left/right buttons are for strafing in these two modes, while keys I and O can be used for turning left/right. Here is a demonstration. As usual, these controls can be customized in js/controls.js.