fix tinymce custom plugins for images and attachments

                                         
|Q            |A                        |
|---          |---                      |
|Bug Fix?     |y                        |
|New Feature? |n                        |
|BC Breaks?   |n                        |
|Deprecations?|n                        |
|Tests Pass?  |y                        |
|Fixed Tickets|CS-5026, IM-1418, CS-5026|
|License      |GPL-3                    |
|Doc PR       |                         |
                                         

Fix few issues related to tinymce and newscoop core changes