[2/3] Telephony: Add Dialer suggestions

Change-Id: I6cb8faee3e6db22cafae283a527d6261efebaf50
Mobile Network Battery Saver Mode

When idle (screen off) switching to 2G can help extend
battery life as 2G generally uses less power than 3G or LTE.

    + 30 seconds after screen turns off, set network type to 2G
    + If a music player is active (playing), do not set network to 2G
    + When device is unlocked, reset to orignial network type

Settings -> More -> Mobile Networks -> Battery saving mode

Change-Id: I34e222ac9e9b3a51a9e4e07f85d0cdc74a99eb6b