Mesh element removal in GUI

This PR integrates functioniality for mesh element removal introduced by @norihiro-w in PR #244 into MeshLib::MeshEditing and GUI.
The functionality is available in MeshLib::MeshEditing::ElementExtraction, the dialog can be accesses in the GUI via `Tools -> Remove Mesh Elements...`
Actual functionality is independent of Qt, the dialog only accesses the editing class. Code is mostly copy/past from the tool by Nori, I added a few details (check if any elements remain in the mesh, ZeroVolume is not tested for `0.0` but `std::numeric_limits<double>::epsilon()`, etc.) and the option to remove elements based on Node position (since I needed this in the past).