Fix font prototype mismatch in SDL-only case

Commit 33bf139002533b2115251e9f391988001dc8fdc3 changed OGL
gr_internal_color_string to take a const char, but left SDL
gr_internal_color_string with non-const char.
Remove extra %i in debugging output
Add editor_status_fmt for printf status messages
Use diagnostic_message directly
Call HUD_init_message_va directly from powerup_basic
Make newdemo_write_string const correct
Add HUD_init_message_literal for preformatted text strings
Fix format string conversion mismatches