some minor cleaning as well

Supporting python 3.8 as well
adding missing field maps for tests
version checker added
version checker needs all deps installed

updated style
fix in lib_tw, was catching the wrong type of error
adding some tests for lib_tw

correcting the amount of data per step in v11 Density_PAR?

Thanks to Ibon for finding this

we do not support python 2 anymore

bumped version to 2.5.0

a lot of blank except: were replaced,
maybe some of them incorrectly

ess.lib_tw is broken due to removing star imports

Update SP_Relativity.py with functions emit_geo and emit_norm which return the geometrical and normalized emittances

bump version to 2.3