dont require clang
added qt5 install to travis config
added apt repo for qt5 to travis config

Travis failed to build before because it couldnt find the
qt5 package
added Qt compile flags to fix errors
cleanup CMake file
updated README with info on dependencies
re-enable travis email notifications

The master branch should be stable now, only break non-master branches!
improved goal-checking in rrt-viewer
added obstacles to rrt-viewer!

Click or drag to make and destroy obstacles

* updated screenshot for README