Changes

[LinearSystem] Cache mapped mass matrix (#4625)

* [LinearSystem] Cache mapped mass matrix

* revert observer pattern

* track mass change using DataTracker

* Verify J is constant by introducing isLinear method

* d_recomputeCachedMassMatrix is now EmptyData

* Comments

* comments

* track changes with DataTracker

* Try to fix Ubuntu compilation

* Missing matrix compression

* Also track mappings