Replace API Explorer

Replace the existing API Explorer (auto generated by django-rest-framework) with a custom data explorer. It will:

• Have the same style as PEDASI
• Show the supported search parameters for a data source
  • Use metadata provided in #40 (closed)
• Help the user to build a search query
• Display the returned data (like the API explorer currently does)
• Allow the user to download the data
• Display the API query which would get the same results