Create mechanism to load data in a separate thread.

Implement ability to stop loading data.

Add documentation to note that loadData and
DataTypeModel.create_data_object are deprecated.

Change name of waveformdialog.py and plottingWidget.py to use snake_case.
Change a name in time_power_squareddialog.py to snake_case.

Rename calendarwidget.py to calendar_widget.py
Rename variables and functions in calendar_widget.py to snake_case

Added missing text box to main UI; fixed erroneously labelled buttons in toolbar; linked calendar buttons in toolbar to calendar dialog

Moved ui.py files into view/ui/; added absolute imports to ui implementations and added sohstationviewer.py as entry point.