Added .cache files in .gitignore

The former ignore rule for .cache files wasn't working for me. Furthermore, I
see no need for using a reg-ex in the specific case.
Updated Eclipse .classpath of partest and scaladoc projects

The version of some of the dependencies used in partest and scaladoc projects
did not match the version defined in `version.properties`. This prevented the
above projects from compiling correctly because the old dependencies were not
available in the local maven repository.
Updated instructions for setting up Eclipse for Scala development
Removed Eclipse .project and .classpath for `plugintemplate` project

According to @gkossakowski this project doesn't need to be imported (and,
furtheremore, importing it in the current form results in errors in Eclipse),
hence I'm removing it.