Add plugin manager dialog to select plugins to load at startup and to call a plugin configure dialog.
Add configure symbol for plugins which is called by Geany when a configure dialog for the plugin is requested, optionally.
Add author field to plugin info struct.
Add sample configure dialog to the demo plugin.
Fix cleanup code in filebrowser plugin to remove it completely when unloaded.			


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2060 ea778897-0a13-0410-b9d1-a72fbfd435f5