Add background option to GlowAdvancementDisplay. Fix client crash

[SHADOWDANCH]

If using 1.12.2 (without forge) client will crash on advancements gui open when on glowstone server. It's related to test advancement and the fact that it doesn't have background set in AdvacementsDisplay.
Here the stacktrace of client crash:

java.lang.NullPointerException: Registering texture
    at cdt.a(SourceFile:215)
    at cdm.a(SourceFile:46)
    at cdr.a(SourceFile:60)
    at cdr.a(SourceFile:42)
    at blx.f(SourceFile:96)
    at bmb.c(SourceFile:138)
    at bmb.a(SourceFile:118)
    at buq.a(SourceFile:1079)
    at bib.az(SourceFile:1023)
    at bib.a(SourceFile:419)
    at net.minecraft.client.main.Main.main(SourceFile:123)

[mastercoms]

Thank you for your contribution to Glowstone!