initial commit on new branch GUI_FileExplorer
Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/
Revert "Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/"

This reverts commit 50ff239f9506ebea7cf2fb3e92f4ee9e7324ba9d.
Revert "Revert "Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/""

This reverts commit adf2205cc6d4e3b01d1ba8bd4f968b98b65b79fb.
add 3rdparty folder to gitignore
Added first version of FileExplorer GUI

filtered such that only folders are visible
Moved FileExplorer from cgsee constructor to viewer constructor
wrapped creation of FileExplorer into Viewer::createFileExplorer()
Fixed showing root directory instead of current working directory in Explorer

* treeView->setRootIndex(dirModel->setRootPath(currentPath));
Added Explorer at the bottom that contains the files in the actual folder
encapsulated navigator and explorer into own classes

* fileNavigator.cpp
* fileExplorer.cpp
ref #10 add first methods to assimp wrapper
ref #10 finish AssimpWrapper::parseNode
ref #10 add parseMeshes method
ref #10 finish basic wrapper; make painter use assimp::wrapper
ref #10 add collada sample file and change camera to look at it
Explorer (bottom) now shows files of directory which has been clicked in the Navigator (left)
changed internal handling of docks for navigator/explorer

* Now the viewer is responsible for creating/deleting the QDockWidget objects
* fileNavigator/fileExplorer is now constructed with its dock as parent
small fix

* added #include <QDockWidget> to libs/gui/viewer.cpp
added test version of context menu when right clicking a file in the fileExplorer