NH4: Split build date from build utilities

This allows makedefs to create verinfo.h for lev_comp and dgn_comp,
which is a version of date.h without the build date info.

Compared to NetHack4, this does not make the changes to support aimake
since this branch won't be using it.  The comment in nitrohack_types.h
claiming "CMake just sets UNIX, and only sometimes :)" is wrong; CMake
doesn't add any flags of its own when compiling.  The commit message
claims that this "fixes the problems with cmake where it would rebuild
all the files" but I'm not sure what this refers to specifically.

Build system updates (cmake and aimake)
Alex Smith <ais523@bham.ac.uk>
43a4cbf71040d9156faa38aa062e0c4b04429918
NH4: Support background colors for stacks + stairs

Object stacks are now given a blue background, while stairs, ladders and
magic portals get a red one.  In general, this adds support for
background colors to the interface.  Also, drawbridges now appear as '+'
when closed and '#' when open.

Compared to NetHack4, monster branding is not implemented, since it
causes monsters to look ugly or become difficult to properly see.  The
repeated color checks and magic numbers are also collected into a few
macros for readability, and NAO-style object stack highlighting is
applied.  Unlike NAO, blue objects on top of a stack are automatically
changed to a black foreground so the object type can be seen at a
glance.

Implement background colors in the curses port
Alex Smith <ais523@bham.ac.uk>
b30c90ac4c54a0735e9eb4f3b2f9c2f58da17644
Turn off blink option by default
NH4: View Sokoban walls completely when premapping

This is meant to go with commit cc784daa52 (NH4: track knowledge of door
locked/trapped status).

Map Sokoban walls as if we're viewing them from the correct side
Alex Smith <ais523@bham.ac.uk>
4905bc7cd9780c005e9b6d88c7887d1c4ceaccac
NH4: Configurable terminal color mapping

The 16 logical NitroHack colors can now be remapped to displayed
terminal colors of the player's choice using a custom colormap.conf file
in NitroHack's configuration directory; an example file can be found at
doc/colormap.conf.

Also, NitroHack will no longer remap user-set terminal colors, and the
darkgray option will make foreground black appear the same on any
background instead of only on the default background.

Color mapping
Jared Minch <jmminch@gmail.com>
1fe9c0fd58cbd14a7b181e78a8561f144ea0e485
NH4: Show levitating, unarmed and trapped statuses

Compared to NetHack4, these statuses are also given colors in the
interface, like existing status effects.

New statuses (levitating, unarmed, trapped)
Alex Smith <ais523@bham.ac.uk>
fd746b75343d615c4eedce2ba4d4752bf687e269
CS1291: Show in status when standing on Elbereth

This also extends the internal maximum number of statuses that can be
transmitted between the game and the interface from 12 to 16.
Show "Elbereth" in Ctrl-E message

I added this Ctrl-E feature while going through UnNetHack revisions, but
used code from NetHack4.  Apparently UnNetHack's code shows "Elbereth"
in the engraving message while NetHack4's code does not.

This is meant to go with commit f791887f2c (CS547 allow engraving
Elbereth with Ctrl-E).