Velocity interpolation order 0 fix

[ChiCheng45]

Description of work
Fixed temperature, DOS and vacf jobs so that they use velocities with order=0. Updated GUI so that the interpolation order choices go from 0-5. Order=0 is only available when velocity data is available. Order=0 is the default if available.

Fixes
Fixes #360

To test

• Load up a trajectory without velocity data in the GUI and check that the possible values of the interpolations order is 1-5.
• Check again but with a trajectory with velocity data. The interpolations order values choices should be 0-5. Defaults should be 0.
• Run a job e.g. temperature with order=0. This should work with issues.

[MBartkowiakSTFC]

I tried it out on a few trajectories. Everything worked as expected.