Added placeholders across the application
Closes #750 (closed)
Added a group of placeholders for when content sections are empty, as well as buttons for taking action to resolve.
I've tried to keep this pretty consistent across the application, but some things may need improvement and some other things may need some more thought re: access. As a rule of thumb I've tried to keep access in line with other components on the page.
Edited by Ciarán Ainsworth