Project stats dashboard should use Entity data where appropriate, fallback to submission endpoints

[manjitapandey]

• On the project submission / stats dashboard we could actually use the already existing Entity data for quite a few things:
  • Total features mapped can be determined from the number of Entities with status > 0
  • The 'validated vs mapped' graph.
  • Expected count & Submission count.
  • Etc
• The main thing that Entities cannot be used for is getting the actual form data, or the user who submitted the feature.
  • In these cases we need to call the submissions endpoint from ODK Collect (i.e. the FMTM submission endpoints).
• The Entity data should be used to quickly populate the stats page, with additional data loading in the background that relies on submission data.
• We probably no longer need to cache the submissions in the S3 either, as we use a single form for submissions & it's relatively quick to return.