initial state widgets forced to sum to 1 even if not appropriate / incorrect error message methodology used

[jarmarshall]

In _format_advanced_option() initial state widgets are forced to sum to 1 without checking if this is appropriate; if the system is not conserved _constantSystemSize == None or == False then user-provided values should not be altered

Additionally, the warning message is printed; the appropriate way to raise errors such as this is via the _errorMessage widget, accessed via _showErrorMessage()

[joefresna]

Problem with exceptions and warnings has a dedicated issue #352