UserIO: AddItem Function

- Added AddItem
- Added buffer flushes after cin uses
- Added all files from main project. Necessary. Simply using the include
in the properties of the project does not do what is necessary.
- Fixed bug in string prompt where whitespace trimming wasnt working
when you had whitespace on both sides
- Switched GetMainMenuChoice to use IntPrompt
-- Fixed PrintItem so that cost would display as $00.00 instead
of$00.000000
- Added AddItem test cases to test project.
- Increased TestSuite test max to 40