Add schema check of task-map entries

[lbradstreet]

The task map entries are getting more complicated over time, and we're having to add validation for kvs that are changing between versions. We should add a schema check for task maps entries to make this process easier.

Schema checks should be relatively non-strict, i.e. they only check the keys and values that are known about by the plugin, and ignore any additional keys.

[gardnervickers]

These were moved up a level to the task bundles. I did not want to have the schema validated twice. @lbradstreet if that's acceptable we can close out this issue.