Minor feature enhancement for 4G LTE Modem(LB2120) admin overview screen

[wonder_trout]

The admin overview screen currently allows users to type in their monthly allowance and then the display shows how much data has been used within the current period. 

It would be very useful to have a simple 'fuel' gauge to indicate whether current usage is likely to sit within monthly usage or likely to exceed it. This could be as simple as a colour indicator on the connection graphic - e.g, red if data is unlikely to last the rest of the period, green if it's within the bounds of possibility and yellow if it looks like it might be getting close to the wire.