ecmwf-api-client ImportError after following the installation instructions for the hyperspectral part of SICOR

The installation instructions in your README.rst suggest to install the ecmwf-api-client only if the multispectral part of SICOR needed. However, since SICOR imports the ecmwf-api-client on the module`s top level here which is executed at the package import time an ImportError is raised if the ecmwf-api-client is not installed.