Added support for custom text colors in gtkrc

[MatthiasValvekens]

I added four named colors (color-normal, color-notfound, color-unique,color-notunique) to replace the hardcoded constants in main.cc. This allows the user to set custom values in his/her .gtkrc-2.0 file. The old constants are used as fallback values. I've also named the GtkLabel attached to the prompt.

Sample config:

style "gmrun-window"
{
  bg[NORMAL]= "#111111"
}
style "gmrun-text"
{
  color["color-normal"] = "#babdb6"
  color["color-notfound"] = "#ff6565"
  color["color-unique"] = "#98c778"
  color["color-notunique"] = "#3465a4"
  fg[NORMAL] = @color-normal
  font = "Terminus 8"
}
style "gmrun-compline" = "gmrun-text" {
  base[NORMAL] = "#babdb6"
  xthickness = 0
  ythickness = 0
}
widget "Msh_Run_Window" style "gmrun-window"
widget "Msh_Run_Window.*.Msh_Run_Label" style "gmrun-text"
widget "Msh_Run_Window.*.Msh_Run_Compline" style "gmrun-compline"