find_file contained a lot of code for searching textures in ways that
haven't been relevant for years. For example, it had workarounds for
MCPatcher, a tool that hasn't been updated since 2015.
Instead of searching in multiple paths that will never succeed in a
resource pack and Minecraft version that actually work, just look
for the filename that the block functions ask for.
Also, if we already have a manually specified resource pack open,
we shouldn't repeatedly re-open it. Furthermore, it's best if
the very first thing find_file does is try to find the file in
the resource pack or client jar we've already opened previously.
We can now also remove chest.png, ender.png, foliage.png, grass.png
and normal_double.png because Minecraft ships them, so we don't
need to ship them ourselves too. Us shipping them actually hid the
whole find_file garbagefire.
Concerns issue #1604.
This is a "quick-and-dirty fix", you may improve it as I'm novice in Python.
Default files in data/textures have been renamed to reflect changes in new 1.6 texture packs (aka resource packs)
