[Bf-codereview] Fix for #36387, User Preferences "Addons" panel bogs down the whole interface. (issue 13271043)

[ideasman42 at gmail.com]

checked over the patch, in general looks good.

Main issue is I wouldn't touch DNA, think this makes it unnecessarily
complicated and would even accept changes to script paths not updating
until blender is restarted. (or users runs the operator) not ideal, but
I would prefer this to adding any DNA/rna changes.


Also I'd prefer the verb `refresh` rather then `scan`.

* rename WM_OT_addon_scan --> WM_OT_addon_refresh
* addon_utils.scan_modules --> addon_utils.modules_refresh
* def modules(... scan=True),  --> refresh=True

https://codereview.appspot.com/13271043/