cleanup a few different things

[davisshaver]

• Adds composer.json
• Checks for featured image ID before using
• Improves type checking to prevent PHP error

[davisshaver]

Could I get a review/merge on this? 😄

[lewayotte]

Sorry for the delay, just got back from a work trip in San Antonio. Just curious, any particular reason why you're including the composer file? We generally don't use composer for our dev.

[davisshaver]

@lewayotte I gotcha.. My thought is that even though we aren't using Composer for dependency management, adding the composer.json will make the plugin easier to use in a WP stack managed by composer. We just need to declare the name and type in a composer.json and then the plugin can be managed as a dependency in composer.