Add better default configs

[tomnewport]

Include
- cg-default
- cg-user

cg-default should be immutable

cg-user should be persistent

• Save and load a ResidueParameters object
• Save and load a ResidueStructure object
• Save and load an ExchangeMap object
• Save and load a GromacsMDPFile object
• Figure out a folder structure
• Save and load a config object

A nice folder structure might be:

/config-name
    /compositions
        /mitochondrial_inner.json
        /eukaryotic.json
    /exchange_maps
         /POPC
             /POPC.json
             /POPG.json
         /POPG
            /POPC.json
            /POPG.json
    /parameters
         /POPC.itp
         /POPG.itp
    /structures
        /POPC
            /<anything>.gro
        /POPG
            /<anything>.gro
            /<anything>.gro