Fixes to text layout

Specifically:
  - Addition of support for TextField#numLines, #maxScrollH and #maxScrollV
  - Addition of huge lists of metrics for many device fonts usually available on Win/OS X/ Linux (we don't get this data from the browser)
  - Usage of proper metrics data to calculate vertical text positioning, instead of just advancing the baseline position by the font size
  - Removal of explicit line breaks during parsing of html instead of during rendering
  - various cleanups, optimizations and small fixes