Increasing z-index of personal toolbar from 1 to 100

Since the personal toolbar is at the top of the page and may include
children that need a high z-index, such as dropdown menus or overlays
we should set it to at least be equal to the highest potential
competitor (the Visual Editor toolbar).

The other option would be to not set a z-index at all, but this would
regress bug 37158.

Bug: 48078
Change-Id: I61daea50209d040f7e0f71207a4e90998c15083f
Merge "Increasing z-index of personal toolbar from 1 to 100"