More careful handling of Nexson meta(data) values

This respects the Badgerfish convention, which says that 'meta' values might not be an array, but an object (singleton) or missing entirely.
Refactored getMetaTagAccessorByAtProperty

This now uses getNexsonChildByProperty, which how also supports the FIND_ALL option.
Refactored array coercion to makeArray() helper
Safer Nexson metadata references: meta() ==> meta

This takes advantage of the support methods and their coercion to arrays where expected, but not guaranteed.
Cleaning up 'rootDist' property from d3.phylogram.js
Merge pull request #143 from OpenTreeOfLife/simple-curation-app

Adapting to Nexson realities, esp. for metadata. Cleanup of d3 'rootDist' properties.