A number of changes around the navigation panel visualization

[xronosuf]

I took a crack at fixing and "improving" a number of aspects - almost exclusively around the nav panel. Included a screenshot below.

Changes:

1. Changed color scheme to include practice and chapter levels. I used a color blindness color palette generator website, so in theory it should be color blind friendly... I have about a 5% faith level in that being true, so Jeff should verify and/or get me the rgb or hex or whatever form of color codes for such a palette choice and I can fix that easily.
2. Rebuilt the practice tile to be horizontal instead of vertical on the nav panel. But this is a little wonky as I didn't want to find the javascript where the actual class values are assigned - so I redefined the "vertical" class to be back to horizontal, since it was always secretly horizontal and then rotated 90 degrees apparently.
3. Rebuilt the progress bar mechanism to work horizontally instead of vertically for the practice progress. While here, I also made the background of the bar visible, so students can see how much they need to fill to get full credit (this has been often requested - weird since it should be clear, but our new nav panel would make it very unclear so it's a good time to do this I think).
4. I added "Practice: " and a CSS qualifier to make the whitespace actually appear, to fix the section number and titles being bound up together, e.g. instead of "3.1.4Real Numbers Are..." it should now honestly show "3.1.4 Real Numbers Are..." in all cases - whereas sometimes it wouldn't before. It also shows "Practice 3" instead of just "3" now.
5. Changed a lot of inheretted CSS values to be precentage based, so that scaling behaves a lot more reliably compared to before. It should actually scale on various size screens a lot better now - still probably not perfect, but should be vastly more consistent at least.
6. Slightly enlarged text in the nav panel as it was small enough to be hard to read by the time you got down to the practice level of tile text, even on a laptop... let alone a phone. This was only a slight increase, so it shouldn't be too much (larger to x-large on top level "part" text, and slightly less text size change between levels to mitigate compounding shrinkage by the time it gets to the practice level text.)

Known Issue:
The practice tile in the nav panel still doesn't act as a clickable link to the practice page (clicking it does nothing) - although you can use the "next"/"previous" buttons at the bottom to eventually get to the practice pages, so they are published and linked correctly. Not sure where this is handled in the nav panel yet - I'm guessing Wim knows more about this though.

Also, this apparently includes the fixes to the server for some translation and setting aria to polite instead of assertive? I thought these went through already, but maybe not? I am now concerned that I made a pull request to the wrong branch or repo.