Direct access to variable data

See merge request es/NES!101

# Conflicts:
#	nes/nc_projections/default_nes.py
#	requirements.txt

# Conflicts:
#	nes/nc_projections/default_nes.py
#	requirements.txt

# Conflicts:
#	nes/nc_projections/__init__.py

Revert "Merge branch 'release-v1-1-4' into 'master'"

See merge request es/NES!99

This reverts merge request !98

- Removed xarray

See merge request es/NES!98

Added some chenges that comes from the raster implementation but there are not related with the raster. Those are code improvements as removing xarray dependence.

# Conflicts:
#	nes/nc_projections/default_nes.py
#	requirements.txt

sum_axis: fixed issue where level was a list instead a numpy array

See merge request es/NES!97

Develop 74 vertical interpolation extrapolation

See merge request es/NES!96