Display library in GRASS 7

Move R_() fns to the display library

Directory lib/raster will be used for raster library. Initial step is to move R_() fns to lib/display.

• lib/raster has been removed in r37976 (lib/raster/raster.c -> lib/display/r_raster.c). The fn names unchanged.
• raster.h merged with display.h
• Some R_() fns can be made be static, see  suggestion (r38001)

Status': done