Feature/gui clean up
Several cleanup related to the GUI:
- removed unused options --> removed unused files
- relocated some files
- the calculated peaks are now displayed differently from observed peaks
- the drawed ellipsoid are not displayed anymore
- the hkl labels of a peak are displayed all over its corresponding frames
The isotope database dialog has also been reintroduced. To do so, the isotope manager class had to be refactored again.