Support commands with options in play plugin

This adds support for specifying additional options in the command config value
for the play plugin. Example:

play:
    command: /usr/bin/command --option1 --option2 some_other_option
Add multi-option command example to the play plugin documentation
MediaFile: allow setting date fields to None
Merge pull request #767 from ghedo/play_cmd

Support commands with options in play plugin
Undo variable name obfuscation (#767)
Fix default config (#767)