DashClock: disable backgroundcolor preference if opacity = 0

To give the user a better UX disable the backgroundcolor preference
if the background opacity is set to 0 (invisible)

Change-Id: I93fc5d1058c1db220c01c3e81b9b45f1eb0316c3
DashClock: Fix menu overflow button on dslv

Usually menu overflow buttons on card or rows are on the top
right on google apps. Follow this UI Guideline and set it as well
to the top right.

And do not cover the whole row height as button to avoid big jumps
of the menu if it needs to show on the top of the overflow button

Change-Id: I2d78ab77249c56935624bca6d1c5949eac1f57b7
Merge "DashClock: disable backgroundcolor preference if opacity = 0" into kk4.4
Merge "DashClock: Fix menu overflow button on dslv" into kk4.4