Add pngs as first class file types in SiteAttachment.
Merge pull request #58 from isaacgrant/pngs-are-people-too

Add pngs as first class file types in SiteAttachment.
Add new SiteBotrMediaCommandLineException and use it everywhere.

This won't cut down on exceptions thrown, but make them much easier to filter out as we usually want to ignore them. Leaving cutting down on exceptions throw until we revisit the encoding pipeline.
Add two more exception types for slightly better exception filtering.

This should allow the filtering we need for now.
Move periods outside of the quoted values in exceptions.

This was a misguided attempt at a consistent punctuation rule, but as @nburka points out, it makes paths and variables look like they have a period in them.
Merge pull request #60 from isaacgrant/filterable-exceptions

Filterable SiteBotrMediaCommandLine application exceptions