Remove plugin symbol configure().
Add plugin symbol plugin_configure() which is used to tell Geany a
widget to pack into the plugin preferences dialog, and connect a
response callback for when the dialog receives a user decision.
This allows Geany to in future implement a common preferences dialog
for all plugins, without breaking the plugin API/ABI.
Add Apply button for plugin preference dialogs (to indicate plugins
should handle the apply response as well as OK, as a multiple plugin
configuration dialog would want an apply button).


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2621 ea778897-0a13-0410-b9d1-a72fbfd435f5