add a unified debug window

[frroossst]

where users can specify the debugger to stop when a register changes or when a certain condition is met like $t0 < 9 or $t0 == $a1

[frroossst]

foundational groundwork: 47f3f08d580fe19d65b01a37f55c6425edf70e6c

[frroossst]

combine with #24, to form a unified secondary view with

• watch expression viewer (also add and remove watch expressions)
• memory visualiser with a table and blocked layout
• call stack
• on the fly modify registers