use IdealForegroundColorBrush in title bar elements

When using a bright theme (such as yellow), you can hardly read the elements in the title bar. With this PR I suggest to use `IdealForegroundColor` where appropriate.

I'm not sure whether I've changed the correct elements. Please review my changes carefully. :worried: 

**Before:**
![image](https://cloud.githubusercontent.com/assets/73690/4781313/75ae5c50-5c97-11e4-8d3f-a0138e778971.png)

**After:**
![image](https://cloud.githubusercontent.com/assets/73690/4781312/42cdf624-5c97-11e4-9fe0-7a31bb537017.png)