Feature/qed disconnected

[RChrHill]

Adds modules for computing QED Disconnected diagrams.

New modules:

• MContraction::QEDBurgerLong
  Evaluates the QED-IB burger diagram with an analytic photon propagator + point-source propagators, with the option to exclude contributions below a certain distance.
• MContraction::QEDBurgerShort
  Evaluates contributions to the QED-IB burger diagram with an analytic photon propagator + stochastic solve propagators within a maximum distance.
• MContraction::QEDSpecs
  Evaluates the QED-IB specs diagram with an analytic photon propagator + quark propagator loops.
• MContraction::QEDTadpole
  Evaluates the QED-IB tadpole sub-diagram with an analytic photon propagator + quark propagator loops. Intended to be used with e.g. MSource::SeqAslash as the emField.
• MContraction::SplitEvenLoop
  Takes two propagator fields solved on spin-colour-diagonal noise sources, alongside their masses, and computes their difference as a split-even estimator.
• MGauge::PhotonPropQedL
  Creates an analytic Feynman gauge QEDL-IR photon propagator in momentum space.
• MUtilities::CShift [with contributions from @mbr-phys]
  Cshifts a propagator field or gauge field by a position vector. The position vector can be passed as a space-separated int string, or it can be the name of an int vector in the Hadrons environment.
• MUtilities::LinearComb [Authored by @rrhodgson]
  Computes the sum of PropagatorFields with coefficients.
• MUtilities::Position
  Stores an integer vector in the Hadrons environment.
• MUtilities::RandomPosition
  Creates a random coordinate vector for the default lattice size and stores it in the Hadrons environment.

Modified modules:

• EmField
  Renamed all "weight" functions to "FeynmanProp" functions.
• MContraction::DiscLoop [with contributions from @rrhodgson]
  @rrhodgson has optimised out the FFTs for inducing a momentum phase, substantially speeding this module up on GPUs. This module has also been extended with an extra template parameter that will enable the computation and storage of the trace of all disconnected loops computed by this module in a vector.
• MGauge::StochasticQedL
  Updated for modified EmField compatibility.
• MGauge::StochasticQedTL
  Updated for modified EmField compatibility.
• MGauge::StochasticQedZeta
  Updated for modified EmField compatibility.
• MIO::LoadField
  Added a reader for ComplexFields.
• MIO::SaveField
  Added a writer for ComplexFields.
• MSource::Point
  Added support for taking the point source position from the environment as a named object.