Upped version to 2.1.0

Version upped due to changes in ProcessBlog and MarkupBlog
Version bump + minor code cleanup

- Version bump to 2.1.0
- Created a link to ProcessBlog config from error message where user
accesses Blog Dashboard for the first time without first selecting a
Blog Style.
Featured image addition

- Version bump to 2.1.0.
- Featured Image.
Implemented this feature by the addition of a third argument to
renderPosts(), i.e., Array $featuredImage.
- Some minor code cleanup.