Story 1563: Typography updates for Tablet

Done in pair programming with Moiz, Kaity, and Vibha

Changes:
* Introduce various LESS variables
* Remove superfluous width rule in common/common.less
* Move rules for .tleft and .tright from hacks to common
as these are not hacks

Change-Id: I14c8182473c9508ffc38a8d5baf114bcb016a35f
Merge "Story 1563: Typography updates for Tablet"