Revert "ISIS-537, ISIS-911 - Remove the extra "Clear" button for Blob/Clob scalars in edit mode"

This reverts commit f605fba1ec596fa79ad9bf63a209114775bf858f.

https://trello.com/c/3ar0leq2/103-my-mistake-we-now-don-t-have-any-way-to-clear-an-attachment-or-blob-if-optional-eg-in-the-todoapp