ui: line chart progress bar

Added a widget which can visualize a list of integers as a line chart and its
usage to the VM main tab for mem/cpu/network usage

Change-Id: I66a577d6e3699c7985a4e6dd4aa66dd5969ebf82
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=803251
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>