When installing a macro, prompt user to install a toolbar button
automatically. Fills in the details of the button using the macro's
metadata, including an icon if the __icon__ metadata variable points to
a file.
Also:
* Support XPM data for macro icon
* Support online icons
* Fix bug in macro uninstall
* Cleaned up macro code
The actual need to restart was removed by 7a566ea4d, this commit
updates the Addon Manager user interface to stop telling the user
they need to restart. Now restarting is only required for addons
that contain workbenches. Macros and pref packs to not need a
restart.