angular distance measurement tool.

- Instead of hardcoding the color Kstars now uses the colorscheme for plotting
  the ruler. This is defined in files .colors under the name AngularRuler.

- The angular measurement tool now may be triggered:
   either pressing [
   or clicking on the right mouse button on a object in the sky and
    selecting the item "Angular distance to....   ["
  and it is finished by:
   pressing ]
   or clicking on the right mouse button on an object in the sky and
   selecting the item "Compute angular distance .... ]"

- The angular distance can be measured on the empty sky when using the keys
  [ and ]. In that case the status bar only will show the result of the
  measurement. If one uses the popup menu one should select a valid sky
  object.

- Now the angular distance measurement mode can be cancelled by pressing Esc

- The ruler is correctly plotted in equatorial and horiontal coordinates mode.

CCMAIL: kstars-devel@kde.org

svn path=/trunk/kdeedu/kstars/; revision=287977