Changed layout of UI to better illustrate workflow in topleft to bottom right progression
QDialog now .show() instead of .exec() to prevent focus
Changed handling of opening MTL file

-Changed "Open" to "Browse" for QFileDialog
-QFileDialog now sets text in QLineEdit
-When "Load" is pressed, now try to parse MTL file
-os.path.isfile check moved to py_fmask.mtl2dict
-If exception, return QLineEdit to previous value
-If no exception, accept MTL filename and fill table
Changed symbology display to QLabel and added spinbox signal/slots

-Symbology color now represented with QLabel background, not text color
-buffer parameters now change with QSpinBox.valueChanged
-Added cloud probability and dilation parameter variables