Improvements for automatically loading many RDF graphs.

* [RDF_GRAPH,NEW] Added rdf_new_graph/2 to come up with variations of graph names in case a graph with the same name already exists.
* [RDF_SERIAL,EXT] Added a clause that applies rdf_load2/2 to a list of file and/or directory names.
* [RDF_SERIAL,EXT] Graph naming based on a given file name has improved, allowing files with the same name to be loaded into graphs with slightly different names.
Added history page to WALLACE.

* [OS_EXT,NEW] Added current_date_time/1, combining date and time into one atom.
* [WALLACE,NEW] Added history (currently of status pane messages).
* [WALLACE,EXT] Changes to the CSS, used in the history page.
Added assoc export to display the results of finding matching properties.

* [ASSOC_MULTI,NEW] Added methods for writing an association list to screen: write_assoc/[1,3] (assuming RDF content, possibly in tuples).
* [PRINT_EXT,EXT] Added print_list/3 to the public predicates list.
* [RDF_EXPORT,EXT] Allow list arguments (RDF tuples) for rdf_resource_naming/2.
* [ASSOC_MULTI,DEB] Added debug statements to put_assoc/4.
* [GRAPGHVIZ,FIX] Argument order in file_name_extension/3 in convert_graphviz/4 was wrong.
* [RDF_GRAPH,NEW] Added rdf_subjects/2 (rdf_subject/2 may return duplicate entries).
* [WEB_CONSOLE,NEW] Added message_web/1 for viewing (part of) the messages history within the Web front-end. Untested!
* [WEB_MESSAGE,EXT] Added message for the case in which there are no messages.