Refactor STAmount:
* Remove unused functions
* Remove unused constructor
* Use delegating constructors
* Mark some observers deprecated
* Clean up declaration parameter names
* Add checked and unchecked constructors
* De-inline unnecessary inlined functions
* Reorder and regroup members into sections
* Move globals from the unity file to the .cpp
* Change some member functions to be free functions
* Put implementation in one .cpp and the test in another .cpp

Remove unused STAmount constructor and delegate two others No change in functionality.
[FOLD] Remove unused STAmount constructor and delegate two others
No change in functionality.