TODO: Write a plugin description
config.extraPlugins = "layoutmanager"
config.layoutmanager_loadbootstrap = true/false (false by default - embedded bootstrap.css is not loaded)
config.layoutmanager_allowedContent (all tags are allowed by default)
config.layoutmanager_buttonboxWidth = 58 (the width of each layout-preview button in the dialog)
Name for adding into the toolbar : "LayoutManager"