SDRPlay Support, Geo-referencing, MetOp X-Band, NOAA MHS calibration and rain map and more

Changelog:

1. Added baseband recorder
2. fixed LimeSDR support
3. Added a plugin system
4. added vegetation index calculation code, not implemented in any decoders
5. Added projections and map overlays
6. TLE Parser for MetOp Admin Messages
7. Support for MetOp X-band dumps
8. Added support for new satellites
9. many small fixes in many decoders (timestamps, typos, etc)
10. Rewrote whole DSP for 2-3x speed increase
11. SDRPlay support
12. Advanced GVAR features, such as crops, temperature measurements and map overlays
13. Fixed mirrored data for NOAA instruments
14. Rewrote NOAA MHS decoder to include calibration

MHS Calibration
NOAA MHS is now calibrated using space and OBCT views. This allows actually using the data for measurements (First step into implementing some actual weather prediction/monitoring tools into satdump!) At the moment, the calibrated data is not saved, but it is available through the get_calibrated_channel() function. It returns a CImg of double values which represent the temperature in K.