completely rewrote all doors code to condense them
into two files - one with the nodebox models, and one with the
actual node definitions.

In the process, cleaned up the code that handles node_ownership
and protection mods.

Also made the mod automatically enable either left-click or right-click to
open/close a door, depending on whether the game supports it (actually it
checks for the existance of an unrelated function that happened to be added at
the same time as the new right-click function).

Renamed some textures, duplicated all of the _lr.png textures to make it
easier to register the textures in a loop and to allow for more flexible
texturing.
Added the ability to place a sign onto a brass or wrought iron fence
uses code from PilzAdam's rework of thexyz's signs mod.
got rid of inventory images for signs - the rendered nodeboxes look better
fixed hacky on_rightclick/on_place code for doors.  They work better now.
got rid of commented-out code
Add ability to place a sign directly onto a brass/wrought iron fencepost

rather than crafting a sign-on-fencepost from one of each, how about just
placing a sign directly onto a fencepost instead?  This commit adds this.
Place a brass or wrought iron fencepost, then attempt to place a sign against
it.  The fencepost will be replaced with one bearing the sign - in the same
node.  Dig to get the two pieces back as separate items, right click the placed
sign to edit the text thereon.

Note that as of this commit, there is a bug in minetest/builtin/item.lua that
causes signs not to be deducted from your inventory on placement.
took fences-with-signs out of creative inventory
made signs check for node ownership/protection before allowing placement.
changed glowlight recipes to avoid conflicts with moreblocks, made IC rely on
moreores copper, added recipes to craft glow cubes back into glowlight slabs.
added alternate crafting recipe for glass-and-wood grid-style doors
Added locked store-able nodes