Timeline Container Highlight Update

Moves the highlight to the timeline container object itself so the whole delegate is highlighted. This was suggested for compact mode but I also left it visible for bubble as I think it still works and adds some user feedback.

Fine tunes the hover actions as follows:
- In compact mode as long as the screen is wide enough they are inset further so they don't overlap the up and down buttons.
- In bubble mode for a user message on the right they are inset slightly further so that they don't overlap the scrollbar

Fine tuned the spacing around the avatar and highlight.

Based upon the suggestions here #550

Bubble Before - no highlight can be seen
![bubble_highlight_before](/uploads/4417d80d62881ff7256bd18a1760002e/bubble_highlight_before.png)

Bubble After
![bubble_highlight_after](/uploads/817e8c749809bf07362af4c9dcdf7087/bubble_highlight_after.png)

Compact Before
![compact_highlight_before](/uploads/aada5d39cfd69563753e5048bd4c248d/compact_highlight_before.png)

Compact After
![compact_highlight_after](/uploads/d3b6c066e86910e7cd2162a970d77ca6/compact_highlight_after.png)