generalize dynamic style sheet value changing from font-size to everything
Merge branch 'dynamic_style' - generalize style parameter adjustments

the code which previously handled zoom in/out by changing
font-size-body etc. in stylesheets is now generalized.
c._style_deltas is a dict:

  {'font-size-body': 0, 'padding-left-body': 10, ...}

the values will be added to the config settings corresponding to the
keys when expanding stylesheets.