q!test: Add the AMOLED theme to previews

[Nebuleon]

A few recent emoji submissions have had issues with the AMOLED theme available on Discord for Android or were attempting to fix them.

Adding the AMOLED theme to the preview of q!test for static and animated emoji would allow blob makers to test out their creations on the AMOLED theme without necessarily having an Android device to test the AMOLED theme with.

Relevant colours:
Background: #000000
Timestamp: #8d8d8e
Message: #dcddde

Here are some preview images using blobninja.

Currently:

Proposed:

Note that this AMOLED theme preview was made by duplicating the Dark theme's half of the current preview image, then subtracting the Dark theme background using GIMP's Subtract layer mode. It may or may not be suitable for production; if needed, it should be remade.