update theme class to properly use WP_Theme class

significantly simplifies the contents of $config and calls few functions to get data
spacing fixes
getting ahead of myself
add method to determine newest tag. Allow for updating plugin based upon tag
fix for undefined variable
fix for undefined variable
update filter to use 'pre_set_site_transient_update_themes'
use transient in check for tags, return early if no tags and work correctly if only one tag
move comment to block header
not sure this is needed
fix spacing
check for tags and abort early
new method to create array of themes

it appears wp_get_themes() doesn't work under network activation. This method creates an array of WP_Theme objects for all directories in the root theme directory
update README
Merge branch 'refs/heads/feature/plugin-tags' into develop
spacing
spacing
moved to single line for simplicity
README and CHANGES updates
added 'GitHub Branch' header to example in README