Download widget polished and wired up to gp task.

Updated path to map service. Force all ID fields to be strings.

Fixed edit session error.

Support where clauses for string and number ids.
Better handling of selected search results in the download widget.

Added "selected" text next to the number of features when that number is based off of a selection.

Added a "Clear Selection" button to allow users to get back to downloading all features instead of the selected subset.

Closes #143
Fixed linting errors
Merge pull request #176 from agrc/download

Download frontend