Enforce 1 to 1 scaling

[TiKevin83]

The GBC and SGB display modes don't appear to have a way to enforce a locked aspect ratio and/or integer scaling to reduce artifacts. It could be preferable to default the lcd size to multiples of 160x144 with options to unlock the aspect ratio and allow non-integer scale factors.

[torch2424]

Just for slightly more context this is also a consequence of:

#90

and

#89