Updating the version to 1.8.4

• Initial BRW FGE metadata
• Merge branch 'Observatory-Metadata' into 'master'
• Added the previosly deleted line is_gin: False back to the the ObservatoryMetadata file for the YKC observatory.
• Revised the minute definition in ObservatoryMetadata and VariometerMetadata. Removed the ObservatoryMetadata variable from IRISFactory and replaced it with the VariometerMetadata variable and an optional variable that points to the VariometerMetadata module.
• Updated the IRISFactory to support the new VariometerMetadata class. Also removed unnecessary lines of code in VariometerMetadata.py and ObservatoryMetadata.py.
• Added the script VariometerMetaData.py to the geomagio folder. Also updated Obsevartory.py to use the VariometerMetaData dictionary to populate a list of observatories using the Obersvatory class.
• Updated the ObservatoryMetadata and Observatory.py files to point to the default_metadata dictionary only. Also edited the declination_base argument so that it defualts to an int = None rather than 0. This change is reflected in the default_metadata as well. Anywhere declination_base didn't exists or equaled 0 is now set to 'declination_base' = None