[Bf-python] Python API proposals

[Dima Glibitsky]

Hi, yet another proposal:

Some scripts need to store their global settings with .blend file, but
currently there is no way to do it reliably (properties added to
WindowManager are not saved, and properties added to Screen can become
inaccessible if the screen is renamed or deleted).

- It would be a good practice to have data storage specifically for
this purpose, e.g. bpy.data.global_preferences.
- Also, it might be useful to have two types of such storage: one
modifications to which are tracked in Undo history, and one which
lives outside of Undo.
- Perhaps it was already requested, but it would be nice if there was
a tab in UserPreferences, or maybe a separate space type, devoted to
the addons' preferences (this could lessen the clutter in the main GUI
by moving rarely used settings to Prefernces).