Adds keyboard commands to reproduce the last items that were built.

[CCHyper]

Closes #168

This pull request implements four new quality of life keyboard commands;

"Reproduce Last Building" Reproduces the last structure that was built. Defaults to Ctrl+Z.

"Reproduce Last Infantry" Reproduces the last infantry that was built. Defaults to Ctrl+X.

"Reproduce Last Vehicle" Reproduces the last vehicle that was built. Defaults to Ctrl+C.

"Reproduce Last Aircraft" Reproduces the last aircraft that was built. Defaults to Ctrl+V.