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- previously introduced `getOrDefault` as a dictionary _get_ method,
  now complete the transition and use it everywhere instead of
  `lookupOrDefault`. This avoids mixed usage of the two methods that
  are identical in behaviour, makes for shorter names, and promotes
  the distinction between "lookup" access (ie, return a token stream,
  locate and return an entry) and "get" access (ie, the above with
  conversion to concrete types such as scalar, label etc).

When activeDesignVariables are not set explicitly, all design variables
are treated as active. These were allocated properly when starting from
0 but not when starting from an intermediate optimisation cycle
(e.g. running 5 optimisation cycles, stopping and restarting).

TUT: added a new tutorial including the restart of an optimisation run
to help identify future regression

- Failed due to double*Matrix<float> multiplication.

Style changes

- use SquareMatrix with Identity on construction

- use Zero in constructors

- remove trailing space and semi-colons

The adjoint library is enhanced with new functionality enabling
automated shape optimisation loops.  A parameterisation scheme based on
volumetric B-Splines is introduced, the control points of which act as
the design variables in the optimisation loop [1, 2].  The control
points of the volumetric B-Splines boxes can be defined in either
Cartesian or cylindrical coordinates.

The entire loop (solution of the flow and adjoint equations, computation
of sensitivity derivatives, update of the design variables and mesh) is
run within adjointOptimisationFoam. A number of methods to update the
design variables are implemented, including popular Quasi-Newton methods
like BFGS and methods capable of handling constraints like loop using
the SQP or constraint projection.

The software was developed by PCOpt/NTUA and FOSS GP, with contributions from

Dr. Evangelos Papoutsis-Kiachagias,
Konstantinos Gkaragounis,
Professor Kyriakos Giannakoglou,
Andy Heather

[1] E.M. Papoutsis-Kiachagias, N. Magoulas, J. Mueller, C. Othmer,
K.C.  Giannakoglou: 'Noise Reduction in Car Aerodynamics using a
Surrogate Objective Function and the Continuous  Adjoint Method with
Wall Functions', Computers & Fluids, 122:223-232, 2015

[2] E. M. Papoutsis-Kiachagias, V. G. Asouti, K. C. Giannakoglou,
K.  Gkagkas, S. Shimokawa, E. Itakura: ‘Multi-point aerodynamic shape
optimization of cars based on continuous adjoint’, Structural and
Multidisciplinary Optimization, 59(2):675–694, 2019