Switch to Chesto keyboard

This PR replaces the hbas Keyboard.cpp with Chesto's EKeyboard.cpp. This brings this code back up to date with the enhancements / changes that were made to it in vgedit.

Right now, there are two issues with these changes: that there are no longer on-screen space or backspace buttons. In vgedit, the space bar is in the "full" view (which would make it offscreen in the pic attached), and backspace is handled by a regular Button.