Implemented 3D orbits and overhauled UI

[Phim226]

Implemented 3D orbits:

• Orbits now parametrised by eccentricity, radius of periapsis, right ascension of the ascending node, inclination and argument of periapsis
• Reference frame now ECI rather than perifocal. The perifocal frame is now only used during initial calculation of state from orbital elements, which is then transformed into the ECI frame.
• Displayed position and velocity changed to display the components in the ECI frame.

UI overhauled:

• The top level UI is now arranged as Inputs | Figure | Displayed properties.
• Fixed issue where UI elements were overlapping when running the program in Linux.
• UI is now in a dark theme.
• UI is built based on the OS being used (currently it only differentiates between Windows and not Windows).

Additional changes:

• Caching introduced in appropriate astrodynamics calculations to avoid the same functions being called several times when lazily grabbing quantities.
• Fixed bug where the home button sometimes didn't properly return the plot to the original view.