File rewrite from Chris Shoemaker.

[David Hampton]

Log Message:
-----------
File rewrite from Chris Shoemaker.  Adds an API for accessing a static
shared program-wide account-type tree model for simple tree usage.
Adds convenience functions for mapping between the selection state of
a treeview using the static account-type tree model and a account-type
selection bitfield.

Tags:
----
gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/gnome-utils:
        gnc-tree-model-account-types.c
        gnc-tree-model-account-types.h