Support mime types with wildcard as subtype in formatter config

This allows to register a formatter for all files that match a certain
media type, e.g.:

  [formatter "PLAIN_TEXT"]
    mimeType = text/*

Change-Id: I5dacf1270501e0608fe115cb924448ef3df76782
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>