Scipion-em-relion

- Postprocessing now supports half maps input
- emtable requirement updated
- close 325 by providing some column types to particle Tables

- Relion 4.0 support:
- download sources from github
- all protocols updated with new args / params
- new 2D class ranker protocol (test still missing)
- new env var RELION_PYTHON for Python with Torch & Numpy modules (required for the protocol above)
- separate initial model protocol for 4.0 (3.x is incompatible)
- float16 option disabled
- EER enabled, needs more testing
- BUGFIX: wrong shifts were saved in motioncor when skipping frames
- rlnMicrographStartFrame is saved in optics for mc output movies
- Multi-body protocol improvements, viewer added
- Postprocessing now supports multi-body input

- allow to use Environ.setPrepend (depends on scipion-em/scipion-pyworkflow238) to set different prepend commands (e.g when optimized CPU module is available)
- fixes for subtract no relion protocol
- fix 294, 296