Improve dashboard/account charts and tooltips

[ahatzz11]

This PR fixes/improves some of the UI around charts for both the dashboard and the account view.

• Fix the tooltip account value text on the tooltip to use color-black for visibility in dark mode. I'm not sure if we want a different tooltip all-together on dark mode, but this is at least an incremental improvement
  

• Changes the circle outline on the tooltip to an arrow. I'm quite colorblind, and the small outline of a red/green circle is almost impossible for me to tell unless I zoom in really close. I think the arrows are a much better visual indicator
  

• Simplifies and consolidates some of the logic/structure around the trend change line. Previously, the net worth chart was using the _trend_change partial, and the account page was rolling its own. This resulted in a few differences:

  • Cool mono font on net worth chart, not on account page
  • Trend % and icon on net worth chart, not on account page
  • Better comparison labels on account page, not on net worth (e.g. "no change vs prior period" for no change instead of "no change vs {selected time period}"

  Now, both charts use the same partial, which was also updated to include the comparison label in a consistent way. This also standardizes a bit of formatting here. The comparison label here is an optional parameter to support places that this partial is used without a comparison timeframe, e.g. the holdings drawer (see more below)

  Account trend change before/after:
  

• Cleans up a few things on the holdings page and drawer:

  • Changes "Cost" to "Average cost" in the table
  • Standardized some locales, although uppercase ends up overriding most of these changes
  • Changes "Trend" in the drawer to "Total Return". This does use the _trend_change partial which is maybe a little misleading, but it doesn't pass a comparison label so there is no vs. comparison. The @holding.trend object here seems to automatically be set to have a start date since the beginning, and the range picker on the graph does not impact the holding page right now, so I think "Total Return" is more accurate"
    

• Adds some text to locales files to the net worth and account charts to remove hardcoded text (there are probably still lots of these, but again just some incremental changes)

[zachgoll]

Agree with all of these! Nice changes.