Formspec Theming

[ghost]

This pull requests addresses changes to transition Unified Inventory away from it's own theme and instead use the default/prepended themes. This allows the inventory formspec to remain consistent with other formspecs provided in the default mod, such as the furnace. It also means less effort is needed when creating or modifying pages because custom background images aren't needed; inventory slots can moved around without modifying images.

Areas that have been addressed:

• Background images removed from the code
• List colors removed
• Use default furnace GUI arrow for pointing to crafting output
• Formspec prepends are allowed by default (to get theming from the default mod), but they can still be disabled if explicitly set to false

Areas of concern:

• Other mods can add their own pages and custom backgrounds. An example is the 3D Armor mod. If this happens, the page looks weird/ugly. A workaround that I implemented is to set the default GUI background after the page formspec code to essentially cover any backgrounds set by mods. The idea would be to keep this in place until we can notify mods using custom backgrounds of the new changes. After most mods transition, we could remove the hack.
• Some mods might use the background images in Unified Inventory instead of creating their own. For that reason, I have not removed any textures from the mod. When the time comes, we could either remove the textures, or change them to 1x1px transparent images that way any mod using them won't have missing textures and it won't interfere with the look of the formspec.

I have attached a few pictures showing what the current formspec looks like. The 3D Armor mod has not been changed in the screenshot. It still has it's own background in it's code. It's the hack mentioned above that covers that up until mods have time to adjust.

Any other thoughts?

[SmallJoker]

Looks gorgeous.

[SmallJoker]

Rebase needed, author is gone and another style change happened already. Closing.