Add public method to remove a study, given its ID.
Version bump of Maven Shade plugin to 2.1

This was required for compatibility with Maven 3.1, see:
https://cwiki.apache.org/confluence/display/MAVEN/AetherClassNotFound
Add method 'unindexNexsons' to oti API

This removes one or more studies by id.
Add ```unindexNexsons``` method to README
suggested changes to unindex method; python3 compliance and bug fixes for indexing script
adding error reporting for failed deletion attempts
Merge pull request #12 from OpenTreeOfLife/remove-study-by-id

Add public method to remove a study, given its ID.