Fix default font algorithm for Windows

Use default system UI font face, and sort out the sizing issues.
The Windows native font description string uses pixels, not points, so we must read the pixel size and save it there.
Change statusbar font sizes for new Windows sizing
Fix ChartTexts text sizing
Fix some text sizes for cross-platform consistency

Using fixed 12pt text makes it too small on OS X (where default is 13pt) and too large on Linux and Windows with the new corrected sizing algorithm (default is 9pt).
These changes use the platform default size as OCPN's default.
more font tweaks, mostly for Windows
Merge pull request #201 from CaesarSchinas/fonts

Fix font sizing for cross-platform compatibility