Merge of the GUI branch

See merge request !102

- Added more documentation to HelperFunctions, Polygon2D, and Color.

- Now ignoring the output and screenshots folders.

- Updated README.md to mention the GUI, Qt, and ORCA.

- Now drawing the bounding-box of a toric world.
- ZoomToFit() uses this bounding box as well.

- HelperFunctions: Added functions for checking/creating directories, taken from CSVWriter.
- Cleaned up CSVWriter accordingly.
- OpenGLWidget: Screenshots and CSVs are now added to a folder that is automatically created.

- Fixed the behavior of several GUI elements.
- Bugfix in CrowdSimulator::StopCSVOutput().
- CSVWriter: Added the "flushImmediately" variable, which is required for the GUI application.
- Screenshots are now written to a different folder.

- CMakeLists: Fixed reference to the Qt resources folder.

- Total simulation time is now stored as a double.

- Changed CMakeLists accordingly.

- Added a project with the necessary files.
- Updated CMake settings.
- Added 3rd-party code for polygon triangulation.
- Added tools/Color and tools/HelperFunctions.
- Vector2D: Added code for disk approximation.
- Renamed WorldBase::Type values, due to naming conflicts with Qt.
- Moved some code to Library and ConsoleApplication subfolders.

Performance improvements

See merge request !101

Made the -o argument (output folder) optional, so that you can run high-performance simulations without storing the results.

- Agents are now stored in an unordered_map.
- Reduced copying in several Vector2D operations.

Removed Agent::getNeighborSubsetInRange() due to performance issues. Cost functions should now perform their own range checks.

The methods x() and y() are no longer needed.
With the correct use of const, it should be impossible to affect vectors accidentally.

Agent::getNeighborSubsetInRange(): Added an efficient shortcut for when the requested "subset" is simply the entire set of neighbors.

Bugfix #86

Closes #86

See merge request !99