using eigen middleCol and middleRow functions

[JensWehner]

This PR does two things:

a) use middleCols middleRows instead of block
b) Refactor the Handling of AOValues evaluated at gridPoints to be more functional

[JensWehner]

@votca-bot changelog: use middleRows/Cols and refactor numerical integration

[codecov]

Codecov Report

Merging #732 (090c9a7) into master (9cfeb74) will decrease coverage by 0.0%.
The diff coverage is 91.5%.

@@           Coverage Diff            @@
##           master    #732     +/-   ##
========================================
- Coverage    51.7%   51.6%   -0.1%     
========================================
  Files         291     291             
  Lines       27050   27031     -19     
========================================
- Hits        13988   13971     -17     
+ Misses      13062   13060      -2     

Impacted Files	Coverage Δ
include/votca/xtp/gridbox.h	96.1% <ø> (ø)
src/libxtp/dftengine/dftengine.cc	71.3% <0.0%> (ø)
src/libxtp/gwbse/bse_operator.cc	100.0% <ø> (ø)
src/libxtp/gwbse/gwbse.cc	0.0% <0.0%> (ø)
src/libxtp/gwbse/rpa.cc	94.0% <ø> (-0.1%)	⬇️
...xtp/numerical_integration/amplitude_integration.cc	90.9% <ø> (ø)
...ibxtp/numerical_integration/density_integration.cc	72.4% <ø> (ø)
src/libxtp/numerical_integration/vxc_potential.cc	75.9% <ø> (ø)
src/libxtp/self_energy_evaluators/sigma_exact.h	100.0% <ø> (ø)
src/libxtp/self_energy_evaluators/sigma_exact.cc	78.4% <83.3%> (ø)
... and 10 more

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[JensWehner]

@votca-bot format

[JensWehner]

@votca-bot format

[rubengerritsen]

Nice, increases the readability a lot