Compiler warnings in PhasorDynamics tests

[pelesh]

Compiler produces warnings when building PhasorDynamics tests, e.g.,

In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/tests/UnitTests/PhasorDynamics/runBranchTests.cpp:1:
In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/tests/UnitTests/PhasorDynamics/BranchTests.hpp:6:
In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/src/Model/PhasorDynamics/Branch/Branch.hpp:11:
/lustre/orion/scratch/nkouk/stf006/Codes/GridKit/src/Model/PhasorDynamics/Component.hpp:51:22: warning: 'nnz' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
        virtual IdxT nnz()

In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/tests/UnitTests/PhasorDynamics/runBranchTests.cpp:1:
In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/tests/UnitTests/PhasorDynamics/BranchTests.hpp:6:
In file included from /lustre/orion/scratch/nkouk/stf006/Codes/GridKit/src/Model/PhasorDynamics/Branch/Branch.hpp:11:
/lustre/orion/scratch/nkouk/stf006/Codes/GridKit/src/Model/PhasorDynamics/Component.hpp:56:22: warning: 'hasJacobian' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
        virtual bool hasJacobian()

Originally posted by @nkoukpaizan in #63 (review)

[nkoukpaizan]

Addressed in #71. Closing.