Use GlyphRun instead of TextBlock for painting clock numerals.

Use glyph-based text rendering inside the clock control instead of
simple TextBlocks. Allow clock numerals to be drawn, styled, and layered
uniformly with the rest of the clock geometry and improve positioning of
clock numerals.
Introduce "office" theme for clock control.

Play with gradients and throw in a bit of yellow/beige for that workaday
office look. Also make necessary changes to support multiple styles in
control resource dictionary. As of this commit, the clock supports two
themes: Barebones and Office.