Merge pull request #8 from IsabellaP/develop

bugfix
bugfix
Merge pull request #9 from IsabellaP/develop

Source Class for Geoland SWI data
bugfixes
updated poets base class, removed dependencies on settings file
added method to download and resample all sources given in self.sources
fixed bug that occured if no host directory was set
deleted settings.py, updated grids, netcdf and resampling to work
without settings.py
bugfixes
removed references to depricated settings file, updated documentation,
fixed bugs
removed unused parameters lon, lat
added column name in output dataframe of zscore method
altered column name of output dataframe
download function now takes poets class start date attribute as default
start date
created unit test for poets.timedate modules, bugfixes in modules
bugfix in unit test
removed depricated sources
bugfix
added new class for regular grids, removed depricated grid classes,
updated unit test for grids
save_image function now works with any temporal resolution, added unit
test for save_image