Removed hard coded message strings from scripts and moved them to the language file.
Fixed a display bug in multimenu field.
Removed rounded help buttons from fields, made the fields use html title to
display the descriptions instead.
Fixed bug for empty muti menu and multi checkbox fields.
Added "Choose..." as first item in single selection menu. Added relevant
string in en language.
Updated /mod/data/lib.php, function store_data_content() so that we store
empty content for fields too.