build: Provide AppImage package for Linux (issue #279) (#945)

* Create AppImage package using linuxdeployqt in Travis CI
* Renamed appPath() to sharedDataPath()
* Fixed include error in tutorial

deployment/dockerfiles/linux/travis_ci/entrypoint.sh

@@ -14,5 +14,8 @@ git checkout $1
 
 ./script/build.sh release test
 
+./setup/Linux/createAppImage.sh
+
 mkdir release
 cp ./Sourcetrail*.tar.gz ./release/
+cp ./Sourcetrail*.AppImage ./release/