Disallow rule create with no distributions; update imports

[markphelps]

Fixes: #758

• Disallow rule to be created with no variants/distributions in UI
• Fix small issue where clicking 'Choose Variants' again didnt clear our distributions
• Update imports from lodash to use ES6 style

[codecov-commenter]

Codecov Report

Merging #759 (12f5588) into master (549104c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #759   +/-   ##
=======================================
  Coverage   82.56%   82.56%           
=======================================
  Files          19       19           
  Lines        1709     1709           
=======================================
  Hits         1411     1411           
  Misses        249      249           
  Partials       49       49           

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