Adding EnsurePropertyIndex component factory

This pull request adds a component which allows for a configuration-based approach for creating Oak indexes. Indexes are created/updated if necessary. An update sets the reindex flag.

This is only dealing with property indexes. I would plan to add ordered index support separately. Since each index type has its own configuration properties, IMHO it makes sense to keep these as separate configs vs. trying to do all index types with a single component factory.

![image](https://cloud.githubusercontent.com/assets/65906/4143849/ec15dbb8-33d2-11e4-879c-d48dec624aac.png)

WDYT about a `log.info` message here?