Fix obs column headers.

[john-michaelburke]

No description provided.

[john-michaelburke]

I'm not sure what this was for so I removed it? Maybe it needs to stay? @samvrlewis

[samvrlewis]

Looks like it was added in this commit by Keith: 764a689

• Adds a line bounding the bottom of the TableView. Allows the user to
  more clearly see the end of the visible portion of the table, even
  when the rows visible do not end at a whole row.

Maybe worth keeping?

[samvrlewis]

This looks good, and I think was similar to what I originally tried (just copying from another table in the app) however I needed to swap out the HorizontalHeaderView for a repeater with rectangles so that the table heading would still appear even when the table was empty. I also wanted to have some empty space behind the table to make it look like a table, even when empty. So that it'd look something like this when empty.

It seems like it's potentially not worth the effort though as it was really hard to get it playing nicely with the resizeable headers and getting the backing white rectangle to be sized the same as the table as the table was resized. I think it's probably fine as implemented here:

I think I'll readd the bottom transparent rectangle and then merge this back into my branch, we can probably leave it as a further later optimisation to show the empty table.