settings.py and settingsdialog.ui:
- added QgsTaskAsync
- added QgsTaskBlockSize
- added BandStatsSampleSize

mapcanvas.py: MapCanvas
- stretchToCurrentExtent returns bool if stretch found an bbox intersecting raster layer

mapvisualization.py
- fixed default sensor specific stretching

updated QPS:
- crosshair shows unit even in case of CRS without description
- small relative import fix in utils.py
- improved checkWavelengthUnit

temporalprofiles.py
- fixed invalid index error for PlotStyle combobox in case TemporalProfiles are deleted
- modified profile background loading, should be much faster now

timeseries.py
- added TimeSeriesSource.clone()
- added TimeSeriesFindOverlapTask to find images with valid pixels within a spatial extent
- added convenience accessors