graphics: nx_openwindow() and nxtk_openwindow() now accept an addtional 'flag' parameter. This argument is not used at present but will, eventually enable a RAM backed, per-window framebuffer.
graphics/Kconfig: Add configuration to support a rambacked framebuffer. Current marked as EXPERIMENTAL because this is a work in progress.
Squashed commit of the following:
libs/libxx: Fix some confusing in naming. If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
libs/: Fix paths in moved library directories.
libs: Brute force move of libc, libnx, and libxx to libs. Cannot yet build it in that configuration.
