Merge pull request #33 from potree/develop

Develop
Merge pull request #35 from chiccorusso/clion

Added .idea to .gitignore. Builds with JetBrains CLion.
Merge pull request #50 from potree/develop

Develop
Fix non-void-return error in PotreeWriter.cpp
Merge pull request #53 from tigerfoot/issue51

Fix non-void-return error in PotreeWriter.cpp issue 51 & 52