restructure tsLogo to allow setting a mask to be used when drawing the
logo dots, as well as add an overlay icon, such as the arrow when
connected to an exit node.
The icon is still renders as white on black, but this change also
prepare for doing a black on white version, as well a fully transparent
icon. I don't know if we can consistently determine which to use, so
this just keeps the single icon for now.
Updates #1708
Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <will@tailscale.com>
2bdbe5b2ab