Add "Clear VM" button to the IDE

[terryzfeng]

Clear the ChucK Instance for public class re-instantiation
feature request from @tae1han

[terryzfeng]

@tae1han Won't be working on this feature since there would be some sensitive VM things that the IDE needs to preserve like HID functionality and the like.

Although not recommended, you can manually clear the ChucK VM with code by doing:

Machine.clearVM(); // Note this would break HID

Hopefully #18 will be able to achieve a similar result as clearVM and maintain WebChucK IDE classes/VM basic things