support FORCE date information for timeseries plots

[Andreas Janz]

Reported by @{5ba7eaba8b5ecf6d0bd9d6da} via email.

bandwise date information is stored inside raster band metedata item FORCE/Date

Band 45 Block=3000x300 Type=Int16, ColorInterp=Undefined
  Description = NA
  NoData Value=-9999
  Metadata (FORCE):
    Date=2017-06-05T00:00:00.0Z
    Domain=EVI
    Scale=10000.000
    Sensor=SEN2A
    Wavelength=2017.425
    Wavelength_unit=decimal year

‌

[Andreas Janz]

example file:

\\141.20.140.222\endor\south-africa\level4\mosaic\2015-2017_001-365_HL_TSA_SEN2L_EVI_TSI.vrt

[Andreas Janz]

VRT has no metadata attached, use different file:

\\141.20.140.222\endor\south-africa\level4\X0007_Y0007\2015-2017_001-365_HL_TSA_SEN2L_EVI_TSI.tif

[Andreas Janz]

@{5ba7eaba8b5ecf6d0bd9d6da} FORCE metadata is now supported

Note that the required changes have only affected the depending RasterTimeseriesManager plugin!