Added API to shutdown the server.
Added API to shutdown the server.

DDoS/SpongeAPI,AlphaModder/SpongeAPI,JBYoshi/SpongeAPI,kenzierocks/SpongeAPI,caseif/SpongeAPI,joshgarde/SpongeAPI,gabizou/SpongeAPI,SpongeHistory/SpongeAPI-History,boomboompower/SpongeAPI,AlphaModder/SpongeAPI,joshgarde/SpongeAPI,modwizcode/SpongeAPI,DDoS/SpongeAPI,Lergin/SpongeAPI,boomboompower/SpongeAPI,SpongePowered/SpongeAPI,caseif/SpongeAPI,Kiskae/SpongeAPI,frogocomics/SpongeAPI,ryantheleach/SpongeAPI,kenzierocks/SpongeAPI,jamierocks/SpongeAPI,jonk1993/SpongeAPI,JBYoshi/SpongeAPI,SpongeHistory/SpongeAPI-History,jamierocks/SpongeAPI,SpongePowered/SpongeAPI,kashike/SpongeAPI,frogocomics/SpongeAPI,jonk1993/SpongeAPI,modwizcode/SpongeAPI,kashike/SpongeAPI,gabizou/SpongeAPI,Kiskae/SpongeAPI,ryantheleach/SpongeAPI,Lergin/SpongeAPI,SpongePowered/SpongeAPI