Get rid of 'Plugins'

It seems every sub-item in the 'Plugins' sidebar item can be safely moved and integrated into other areas of the UI, where they can be logically grouped. For example: - '3rd Party Adverts' can be moved into the 'Pages' item (as it relates to page content), or alternatively 'Website Settings' (if it is a global setting that somehow changes the behaviour of the entire website) - 'TinyMCE Plugins' and 'TinyPNG Image Compression' should be moved into a 'TinyMCE' category under "Modules" (after all, that's what TinyMCE is). - 'Stock Photos' can be moved into 'Import Tools' (if we see its function as 'importing an image') or 'File Upload' (if we see it as 'uploading an image') - 'SendFox Integration' can be moved into 'Modules'