Merge pull request #66 from gnotaras/enhance-common-objects

Complete rewrite of the part that generates the URLs to be purged.
Use 'manage_options' capability when adding the admin interface.
Improved admin bar menu functionality and fixed bugs.
Moved WPVarnishAdminMenu() after WPVarnishAdminBarLinks()
Merge branch 'enhance-purge-url-pool'
Merge branch 'master' of https://github.com/gnotaras/wp-varnish