Bug 1007709 - [Dialer][Call Screen] Create fluid size for contact name in the upper information panel

Hey! The reason of that renaming is that there is already an activeCall variable defined (see https://github.com/gtorodelvalle/gaia/blob/dialer-callscreen-bug-1007709-fluid-font-size/apps/callscreen/js/calls_handler.js#L774) and I got the corresponding JSHint error :(