Fix #83: Change base texture of BloomCombine shader to a parameter

[rccarlson]

Fix to #83 by implementing this solution

This still doesn't quite work with DirectX, but it's an improvement over how it was.

[CartBlanche]

@rccarlson thanks for the PR. We are looking into it.

[SimonDarksideJ]

FYI, please revert the changes to the MG version back, as this is targeting the 3.8.2 samples branch which are LOCKED to 3.8.2

"version": "3.8.2.1105" -> "version": "3.8.3"

[SimonDarksideJ]

Closed as it was superseded by the fix in #90 which works for both DX and GL