use more residual properties when available

[longemen3000]

this PR:

• changes some methods to only use residual properties (single and multicomponent equilibria), we were wasting extra time evaluating ideal models that were then substracted away (15% improvement on saturation_pressure(PCSAFT("water"),373.15). In multicomponent equilibria, there is a problem with just equating the chemical potentials: the ideal term is of the form f(T) + log(x[i]/v[i]) and their substraction causes numerical problems. combining the two logarithms in one expression seems to stabilize the solver.
• adds a default method for p_scale that uses lb_volume and T_scale. fixes some scaling errors found with p_scale methods for some EoS.
• fix custom definition of virial coefficient for cubics
• merges GroupParam and StructGroupParam into one struct (GroupParam)
• adds the PPDS ideal correlation (PPDSIdeal)
• adds EoSPhase as a potential struct to use for representing phases (the infraestructure to use it across the methods is not yet there, probably we can use a macro to transform between our current methods return type and returning lists of phases)

[codecov]

Codecov Report

Attention: Patch coverage is 79.96604% with 118 lines in your changes missing coverage. Please review.

Project coverage is 76.86%. Comparing base (878c810) to head (92fd3d3).
Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
src/methods/phase.jl	0.00%	61 Missing ⚠️
src/modules/solvers/Solvers.jl	59.37%	13 Missing ⚠️
.../property_solvers/multicomponent/multicomponent.jl	94.11%	5 Missing ⚠️
src/database/database_rawparam.jl	63.63%	4 Missing ⚠️
src/database/database_utils.jl	0.00%	4 Missing ⚠️
src/methods/VT.jl	0.00%	4 Missing ⚠️
...ty_solvers/multicomponent/solids/eutectic_point.jl	0.00%	4 Missing ⚠️
src/database/params/GroupParam.jl	83.33%	3 Missing ⚠️
src/methods/initial_guess.jl	86.36%	3 Missing ⚠️
...rc/methods/property_solvers/multicomponent/VLLE.jl	95.83%	2 Missing ⚠️
... and 14 more

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #297   +/-   ##
=======================================
  Coverage   76.86%   76.86%           
=======================================
  Files         321      321           
  Lines       24049    23993   -56     
=======================================
- Hits        18485    18442   -43     
+ Misses       5564     5551   -13     

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