CMake: improve FindHeeksCAD module
CMake: improve FindHeeksCAD module

  * Use a cleaner method to find from multiple paths
  * Add "/usr/local/share/heekscad" to searched paths: HeeksCAD now install its sources there (with default prefix: /usr/local)
  * Add "/usr/share/heekscad" to searched paths: HeeksCAD now install its sources there (with most linux distributions prefix: /usr)


AlanZheng/heekscnc,JamieFBousfield/heekscnc,ant-t/heekscnc,elliotf/heekscnc,hackendless/heekscnc,FluffyMortain/heekscnc,dnevels/heekscnc,blakelyc/heekscnc,JamieFBousfield/heekscnc,FluffyMortain/heekscnc,dnevels/heekscnc,BbiKkuMi/heekscnc,AlanZheng/heekscnc,masika/heekscnc,pyrotron/heekscnc,AlanZheng/heekscnc,masika/heekscnc,elliotf/heekscnc,hackendless/heekscnc,masika/heekscnc,FluffyMortain/heekscnc,dnevels/heekscnc,Nurb432/heekscnc,pyrotron/heekscnc,pyrotron/heekscnc,blakelyc/heekscnc,hackendless/heekscnc,ant-t/heekscnc,singwina/heekscnc,ant-t/heekscnc,BbiKkuMi/heekscnc,singwina/heekscnc,sangit/heekscnc,dnevels/heekscnc,JamieFBousfield/heekscnc,Nurb432/heekscnc,blakelyc/heekscnc,JamieFBousfield/heekscnc,pyrotron/heekscnc,ant-t/heekscnc,AlanZheng/heekscnc,blakelyc/heekscnc,singwina/heekscnc,elliotf/heekscnc,FluffyMortain/heekscnc,sangit/heekscnc,Nurb432/heekscnc,singwina/heekscnc,Nurb432/heekscnc,elliotf/heekscnc,sangit/heekscnc,BbiKkuMi/heekscnc,masika/heekscnc,sangit/heekscnc,BbiKkuMi/heekscnc,hackendless/heekscnc