Add custom image support for launcher.

[DJ3dyo]

as the tittle says, it would be nice to be allowed to change natively the background image of the launcher for a custom made one when we feel like it, I'm also personally am not a fan of the Painted SIT logo neither.

Here is an example custom image ive made that feels like a better fit for the launcher, if ever it can give ideas.

[artehe]

Depending on peoples thoughts on #257 I'm inclinded to remove the background image as it just causes visual issues which makes things look horrible/hard to read in places.

I do like the image you made and don't particularly have anything against the current one, so I'm trying to think of some nice ways I could use them still in some other places. 😄