Untested secondary TOC gauge

Much of the basic code for the secondary TOC gauge. This code is
untested and may make several invalid assumptions. These will be fixed
in debugging.
Secondary Gauge Box

Secondary Gauge box is working after loads of attempts and maths. I
didn't understand the context drawing methods and ended up having to
redo a bit of stuff.

- Secondary Chapter marks are going far off right (positioning vs
chapter length isn't right).
- Secondary Gauge fill isn't working. (probably same problem.
Minor Fix and Comments

Includes a Minor fix to insure primary gauge is the right color. Also
adds comments detailing why the secondary chapter marks are wrong.

Please note, there were more changes, but were lost due to early morning
git (and github) blues. This commit represents the heart of those
changes. Anything else will need to be re-developed from
scratch...that's assuming there were any worth remembering.
Secondary Bar Filling

- Secondary Bar is now filling properly. Needed to expose current
paragraph index in FBReaderApp (there is probably a better way to do
this, though)
- Chapter marks now mostly working. There is a bug in the scaling.
Secondary Chapter Marks Issue

Either the meter scale, or the secondary marks scale ... OR BOTH ... are
not working properly. It probably has something to do with the
conversion to chapter-relative positions that I am doing.

Even so, this is a lot of progress for the weekend.