NetStats: Don't update stats when screen is off

Also moved registering of broadcast receiver and settings
observer to onAttachedToWindow() and unregistering to
onDetachedFromWindow() to avoid these being leaked.

Change-Id: Ia131a0db65c4c762b7f28493e812f9fb21358a27
NetStats: Option to hide NetStats if there is no traffic

Change-Id: If9626946d31f9a2ac30a3be57a182fb99ef2229f
NetStats: Show "MB/s" instead of only "MB"

Change-Id: I23fa4560a7551495cc4ffa5610c806d4da48f73b
NetStats: Make color settable by user

Change-Id: I9ec49ee9ffe51d07d4930103fa67be2266d41c5c
Traffic meter: Option to choose update speed

Change-Id: Ia61f71a71fc41a13489342fc0f843ae2ec3810cf
Either enable NetStats or Traffic meter

Change-Id: I0c9e21b7eb1a6de5599bd7abc912a61c3c2138ef