New operators (Epsilon, FullStokes), components, blending, cmake

TODO:

• regenerate ops after unused variable issue has been resolved in HFG

This MR introduces several things:

1. New operators (both with and without IcoShellMap blending)

• diffusion (P2)
• gradient (P1 -> P2 vector)
• divergence (P2 vector -> P1)
• epsilon (P2)
• full_stokes (P2)

2. Implements component pass through for vector forms.
3. cmake file generation now only uses present source files. This avoids having to generate everything to also get the correct cmake files.
4. Unused variables warning fixes
5. Parallel operator generation
6. Fixes for single precision builds.
7. Deterministic variable naming for moved constants.