Acknowledging data providers

[znichollscr]

In our outputs, we need to do a better job of acknowledging all the observational networks on which we depend for data. It should be immediately obvious to anyone using the data/visiting this page that it is built on top of the efforts of others and many of the numbers are not purely ours.

[znichollscr]

#78 provides a start. However, we'll need to go gas by gas as many of the networks have papers for individual gases which should be cited.

Best idea for now:

• when a data source is grabbed, create a DependencyInfo file
• when a data source is used in the composite for a gas, load the DependencyInfo file and add it to some gas specific directory of dependencies
• when writing the input4MIPs file, all dependencies in the gas' directory get included in the file's metadata