[v1.06] moved several css settings into user preferences

css rules that are now user-configurable:
  * font-family
  * font-size
  * line-height
  * padding around the body
  * width of indentation for expanded children
    (note: 1.5em is ADDED to the value specified through this setting.
           This is the width required to ensure the expand/collapse
           button can be properly displayed.)