Does not support screen with multiple regions

[samuell]

Steps to reproduce:

• Start showterm with showterm
• Start screen with screen
• Press [Ctrl] + [a], [Shift] + [s] to split the screen vertically
• Press [Ctrl] + [a], [tab] to jump to the other region
• Press [Ctrl] + [a], [c], to create a new window in the new region
• Write some commands in below region
• Press [Ctrl] + [a], [tab] to jump back to the upper region
• Write something in the upper region

Result: Only what you do in the upper region is shown.
See: http://showterm.io/2b3664fe03a2d6e25b311