Default Neo4j Plugin dir to build directory

[StephanPirnbaum]

Currently, Neo4j plugins are stored in /tmp/ if not configured otherwise. This causes issues under Windows as deletion of the plugins happens when there is still a lock on the jar files, leading to plugin not being deleted. Furthermore, it happened that during one build, two different /tmp/ plugin dirs were used, with one not being populated previously.

It would be better to use the build directory by default to store the Neo4j plugins and let Maven clean take care of deleting them instead of doing it from jQAssistant.

To avoid errors of copying Neo4j plugins multiple times into the plugin dir, it shoudl be checked if the file already exists:

at org.apache.commons.io.FileUtils.copyFile (FileUtils.java:859)
at org.apache.commons.io.FileUtils.copyFile (FileUtils.java:812)
at org.apache.commons.io.FileUtils.copyFileToDirectory (FileUtils.java:960)
at org.apache.commons.io.FileUtils.copyFileToDirectory (FileUtils.java:931)
at com.buschmais.jqassistant.core.store.impl.EmbeddedGraphStore.resolveNeo4jPlugins (EmbeddedGraphStore.java:98)
at com.buschmais.jqassistant.core.store.impl.EmbeddedGraphStore.configure (EmbeddedGraphStore.java:80)
at com.buschmais.jqassistant.core.store.impl.AbstractGraphStore.start (AbstractGraphStore.java:70)