User created databases and easy PR submission

[adamkucharski]

Suggestions by @smwindecker and @mgrabow2 highlighted two related features that could be helpful:

1. Would be useful to allow a user to create several local epidist objects (e.g. in a script) then store locally as a epidist_db object (e.g. in JS format), that can then be reloaded.
2. Would be nice for user to take their newly created epidist objects and easiy add to database. This might be easy-ish via PR if the above functionality stores locally in the same format (e.g. JSON).