The updated and installable version of SIAC

Updated to be able to handle various data inputs and make the whole module to be installable.

AtmoCor for Sentinel 2 and Landsat 8 public release 1

Uncertainty propagated Sentinel 2 and Landsat 8 atmospheric correction,

1. Now the 'uncertainties' are propagated and saved as individual files
2. Reduced the memory usage to 16 GB
3. MultiGrid method is used to make it faster and better detailed AOT estimation
4. Python 3.6 compatible
5. Angles are reconstructed per pixel basis
6. Cloud calssfier from https://github.com/sentinel-hub/sentinelhub-py are used to generate cloud mask
7. Landsat 8 correction is now implemented as well
8. Downloaders for the auxilaty files are added