Bug 18750

More like a container task that could depend on other tasks: for 3.4 we should
start to use MIME types consistently for various loaders. E.g.:

- ExtensionList should handle MIME wildcards and understand attributes listed
after a semicolon as being specializations (e.g. "text/html" will match actual
type "text/html;charset=UTF-8")

- XMLDataObject in APIs, as well as in xml module, should recognize text/xml as
well as text/*+xml, and use a MIMEResolver rather than file extension list

- TXTDataLoader should recognize text/plain, and use a MIMEResolver

- ditto HTMLLoader (text/html), ImageLoader (image/*), ....

- CloneableEditorSupport could find the right editor kit using a better lookup
which understands MIME attributes and wildcards, too; e.g. setting its
contentType to text/x-ant+xml should use a text/xml kit if available;
JEditorPane's registration is not so clever

- if we make a meta-loader which delegates to other loaders by MIME type, it
should check first for an exact match, then exact module attributes, then a
wildcard match, etc.