Keep project files out of addons folders.

[bilderbuchi]

When the project generator will be able to generate project files for addons, too (OF issue openframeworks/openFrameworks#1234), we can drop the project files from addons' examples. Then, the following gitignore entries will come in handy.

# Project files should not be committed to the repo. They will (soon) be 
# auto-generated by the project generator.

#XCode
/*/*.xcodeproj
/*/Project.xcconfig
/*/openFrameworks-Info.plist
/*/ofxiphone-Info.plist
/*/iPhone_Prefix.pch
/*/*/*/Default.png
/*/*/*/Icon.png

#Code::Blocks
/*/*.cbp
/*/*.workspace

#Visual Studio
/*/*.sln
/*/*.vcxproj
/*/*.vcxproj.user
/*/*.vcxproj.filters

#Eclipse
/*/.cproject
/*/.project
/*/.settings/

#Linux
/*/Makefile
/*/config.make