Don't raise error parsing MTL file

We sort of handle the error OK by restoring previous MTL filename
text and printing to console. Big TODO will be adding QgsMessageBar
to better display the error
Fixed user nodata value bug & layers not repainting

User no data required a list of QgsRasterRange
Raster layers have cache images you need to delete before repainting
Updated UI with formatting and cloud matching calculation button
Fixed bug where cloud probability wouldn't change

Issue with do_plcloud signal where do_plcloud's 'value' argument
was sent by signal occurred because Python never updates the initial
value after the function has been read in