simplified labeling: uses now mouse buttons to add / remove observation dates from the date collection

* chip view settings
* label settings: add, remove, clear observation labels from selected image chips

recognizes observation date from Landsat scene ID in file names

added setRGBSettings(bands_and_ranges)

paste_band_settings routine to parse band selection and ranges from QGIS style clipboard information

refactoring and more...

ImageChip context menu offers:
- to load the respective scene in QGIS
- to copy the image chip to the clipboard

changed BandView widgets

qrangeslider from https://github.com/rsgalloway/QRangeSlider

new capabilities:
save and load text file based definitions of time series data files
supports multiple sensors in a time series