Hacky support for fitting specs

[jonc125]

• Add a boolean field to ProtocolEntity (well, will probably have to be on Entity actually) stating that this is a fitting specification, not (just) a forward simulation protocol.
• If this field is set, pass extra 'data' and 'fittingspec' arguments when launching experiments using this protocol.
• On the experiments view, add a button to toggle between 'Show parameter fitting experiments' / 'Show simulation experiments' (which will add an extra boolean show_fits to the JSON call)
• Allow owners to toggle it on/off? Initially just require it to be set on entity creation.