Bugfix: /_sites in the getPrefix

Adds /_sites in the getPrefix regex

Feature: Find Component Ref in Page

add findComponentRefInPage which returns the first encountered reference to a component of a certain type in an unresolved page body

Feature: get layout prefixes

update getPrefix so it gets site prefixes from /_layouts/ uris

Feature: Layouts and Metadata

• add isDefaultLayout (similar to isDefaultComponent)
• fix issue with getPageInstance and getLayoutInstance where they don't handle /meta correctly
• add isPageMeta
• add isLayoutMeta

Feature: Layouts

Add methods for _layouts #9

Feature: isUri

• isUri checks for presence of /_uris/

schrodingerian-publishing

• FEATURE: isPublished function #7