Convert save data files from json to csv

[K-Meech]

For #20

This PR converts save data files from .json to .csv format, as discussed in the last meeting. @mmcleod89 and I looked for an existing csv reader integrated into unity, but none appeared to exist - as such, this PR uses built-in functionality like StreamWriter to read / write csv manually.

I wanted to avoid adding lots of boiler plate code to the various GameData classes, so currently all the conversion code is inside SaveData and uses reflection to read / populate the relevant fields. Not sure if this is the best way to do this - so do feel free to change this however you'd like!

Still todo:

• save data is only created for complete games so far. We need to add saving when a game is stopped early via the exit button / quitting.
• This keeps the data saved as-is, but David has made a rough outline outline of extra data he'd need: see issue 20. This needs to be discussed / game data classes updated.