Add a progressbar widget to the statusbar and use it to show progress when building with the Make commands, when printing and when using Find in Files.
Add progressbar convenience functions and ui_entry_add_clear_icon() to the plugin API.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@3517 ea778897-0a13-0410-b9d1-a72fbfd435f5