Add correct icon for overflow menu

- Using vector rather than PNG files to control apk size
- Removing the unused old icon
- The pathdata is obtained from https://icons.googleplex.com/#icon=ic_more_vert&search=dot
- Based on the doc here: http://developer.android.com/tools/help/vector-asset-studio.html
  it makes sense to color icons black and add a tint to the vector drawable.

Bug 25968255

Change-Id: I57c01c44685af0d226fa5876b10f4c44254598ae