Input handling still occurs in scenarios when it shouldn't

[HJPearce]

Description

Pausing the game and constructing a building do not correctly prevent other forms of input

How To Reproduce

Steps to reproduce the behaviour:

1. Open main game
2. press pause
3. attempt to move units

Expected Behaviour

The game should not process unit selections/commands as gameplay is 'out of focus'

Proposed Fix

This can be fixed by adding a sense of 'input layers', where some input processors can be disabled at particular points in time