Tool shed publishing support.

 - New shed_upload command that can tar up a repository and publish it to various tool sheds.
 - Introduce global config file ~/.planemo.yml with optional tool sheds API keys, tool shed username, etc...
 - New config_init command to setup a template for this global config file.
 - Allow each repo to contain an optional .shed.yml describing name of repository (will fill this out with more options).

Have to disable Python 3.4 support because bioblend doesn't support Python 3.4.

Warning: This depends on very new tool shed features that have not even been merged into galaxy-central yet.