Add first version of entity conflict summary box

[matthew-white]

#505 calls for a summary box about entity update conflicts. The summary box has a few component parts:

1. Summary table (to be done in Add entity conflict summary table #529)
2. "Mark as resolved" button and the footer that contains it (to be done in Mark update conflicts as resolved on Entity Detail page #506)
3. Lastly, the header at the top of the box

This issue is to add a first version of the summary box to the entity detail page. For this issue, the box should start out with just the header.