Other minor fixes.

* Add visible clearance when edit node or track segment,
  add parameter "show clearance for new or edited track with via area"
  in "Display options" menu.

Useful in compact designs to know hos to place a via during track creation.

* All: remove all remaining occurrences of g_DialogFont and dialog font menu handers.
* All: remove all remaining non-standard fonts and button text colors from common dialogs.
* PCBNew: remove all non-standard fonts and button text colors from dialogs.
* PCBNew: update project library and path dialog to match changes to CVPCB version.
* EESchema: update project library and path dialog to match changes to CVPCB version.
* EESchema: save vertical/horizontal line direction setting between sessions.

All: cleaning code to draw/plot texts (work in progress). Eeschema: italic and bold texts and labels allowed
(plot functions not yet updated for bold texts)