Add map to query by HUC

[cristinamullin]

Is your feature request related to a problem? Please describe.

Users may not know their HUC code to enter on the import tab. They would like us to add a map to the import tab to help facilitate queries by basin/HUC.

However, the WQP HUC queries are not inclusive of all sites actually available within the HUC (known WQP bug with no immediate plan to resolve).

It may be better for focus on the bounding box map instead. See related issue: #225

Describe alternatives you've considered

Users could use How's My Waterway to find a HUC, and then enter it manually. We could also add the map and include text about the HUC query issues (a warning).

Reminders for TADA contributors addressing this issue

New features and/or edits should include the following work:

• Create or edit the code.

• Document all code using line/inline and/or multi-line/block comments
  to describe what is does.

• Create or edit tests in tests/testthat folder to help prevent and/or
  troubleshoot potential future issues.

• If your code edits impact other functionality in the shiny
  app, ensure those are updated as well.

• Run styler::style_pkg(), devtools::document(), and devtools::check()
  and address any new notes or issues before creating a pull request.