Slimrecents background color && transparency [1/2]

Allow user to specify background color and transparency level
    for the slimrecents panel.

PS: now setting sticks through reboots and TRDS state
        changes. also, add reset to default color option.

PS: when resetting to default, use TRDS (png) resources
        instead of custom color

NOT USED FOR crDroid -> PS: properly set preference summary for default
        value ("TRDS default")

Change-Id: I42ec2c9cf0f65b0dc8936e1cc45f171afe1d6afa
PS: remove LSN dependency