Since Test and Live Pantheon is read-only, check only the status of recorded symlinks

[carl-alberto]

Since Test and Live Pantheon is read-only, check only the status of recorded symlinks and remove the deleting and adding capabilities.

Possible scenarios:

• symlink is recorded in DB but not present in filesystem
• symlink is recorded in DB, link is there but target folder is not yet created

Also add a message warning in test and live something like:

"This plugin is specifically designed for one-time use and when setting up your site in DEV. Once the symlinks are all setup-ed in dev and deployed to your production, the plugin can be safely removed without losing the symlink functionality"