Disassembly keyboard shortcuts and step over

Adds shortcuts to the disassembly view and reassigns a few global shortcuts (see below).
Also extends the step over function, though it doesn' work on conditional branches yet.
There's a summary of the debugger functions in debugger.txt. 

These are the new shortcuts for the disassembler:

Toggle breakpoint		Space
Run to cursor		F9
Step over		F10
Step into		F11

And the changed global shortcuts:

Screenshot		F9 -> F12 (Steam, for example, uses the same key by default)
Toggle fullscreen	F11 -> Alt+Enter (used almost universally in games)