Also upgrade the file picker filters with the new extensions found
in the orginal file picker code of Singularity.
Also improve AIFilePicker a bit: added hasFilename() and now
deleting the statemachine automatically by default: it's no longer
needed to call deleteMe from the callback.
This commit contains all changes, except those in indra/media_plugins
(which was renamed to indra/plugins) and indra/llplugin.
However, it does contain the (new) file
indra/plugins/filepicker/basic_plugin_filepicker.cpp
