Updated to tycho 0.18.1 and Eclipse Kepler
Adds and fixes module to build p2 update site.

The org.datacoalition.yedit.update project had no pom and was designed
to build an old legacy style update site. This commit changes it so
that Tycho is used for building a p2 update site instead. The module
is then added to the parent pom.
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