refs: https://github.com/TryGhost/Team/issues/1462
- moved the delta graph into the revenue graph of the main combined graph
- made the secondary dropdown work again
- updated some chart titles
- tidied up the code and styles to make it work well
refs: https://github.com/TryGhost/Team/issues/1462
- added in dynamic dark mode grid lines for the charts
- added in some subtle other dark mode tweaks for borders
- limited the recent posts to 3 instead of 5