Added options to enable MySQL FULLTEXT support to file 'contact.properties':

Added property com.openexchange.contact.fulltextAutocomplete which defaults to false. That property configures if a FULLTEXT index dedicated for auto-completion can be used or not. Once enabled, an appropriate index is created on the 'prg_contacts' table automatically (covering fields specified through com.openexchange.contact.fulltextIndexFields property), and is used afterwards to serve the find