Build resolves snakeyaml.jar using Maven dependency

The Resources directory of the yedit plug-in is removed by
this commit. The directory contained a checked in version
of snakeyaml-1.8.jar with corresponding source. Now, that
jar is fetched using a Maven dependency instead and then
added to the update site.

This also means a snakeyaml upgrade from version 1.8 to version
1.13