Fix PortMidi pause + some other things

[bsdf]

a couple of bugfixes and additions. let me know if you want me to break these out into separate PRs

• fix issue with PortMidi not unpausing
• fix mouse warping in scaled window
• add integer scaling option
• map left/right to first/last option in menus as in the system35 windows engine

[kichikuou]

Thanks!