Create `destination` Module

[noelworden]

Fields based on existing Google Sheets column

longitude -> decimal latitude -> decimal name -> string description > string(?) icon -> integer spinner_friendly -> boolean lake -> boolean less_than_one_hour -> boolean one_to_three_hours -> boolean greater_than_three hours -> boolean car_friendly -> boolean hike_in -> boolean allows_dogs -> boolean dogs_off_leash -> boolean season_spring -> boolean season_summer -> boolean season_fall -> boolean season_winter -> boolean car_camp -> boolean backpack_camp -> boolean fee -> boolean ice_fishing -> boolean

[noelworden]

Initially, the intention was to create only the module, but then I came across the phx.gen.html generator:

• https://hexdocs.pm/phoenix/contexts.html#adding-an-accounts-context

Curious as to exactly what files it would produce, I used it to create this module. In short, it created every file needed to get this basic CRUD module working, from views with working forms to tests. I felt that having a beginning-to-end example of what files are necessary, I included everything in one PR, as multiple commits, to act as a reference for future work.