Export all dates in one date file

[martenmatrix]

1. Fetch available months
2. Fetch available dates for a month in JSON
3. Iterate over all availabe months and merge
4. Return as JSON
5. Return as date file (maybe a json converter, so it also works for just one month)

[martenmatrix]

api should be simple, conversion is out of scope, represent the same functionality as the stine website