Design polish for table view

[taramk]

Table styles:
https://www.figma.com/file/bGzEZo0NYHhWGJO95kwF3p/Treehouse-App?type=design&node-id=311%3A4643&t=gDnarCqSzNwNgr2i-1

8px = --padding/2
4px = --padding/4

Implementation notes

• header row on table has 8px bottom margin (on text, above horizontal rule)
• horizontal rule below header uses --color-outline-secondary and has an 8px bottom margin, which is the same as nodes have
• entire table has an extra 4px bottom margin (same as .expanded-node class, can consolidate these)
  remove 1px padding on header row cells
• add "Title" header to first column (Tana does this, and it helps balance out the header row visually). header text should be aligned with node text, not node bullet.