Added a plugin whitelist property to control what plugins to install.

While I have most Eclipse language plugins (pdt, cdt, etc...) installed,
I actually prefer YCM+Syntastic for some of those (Python, C++). With
this property I can just say:

-Dplugin.whitelist=org.eclim.jdt,org.eclim.adt

To only install the java plugins.

I remember that a similar functionality was once on the build scripts
but I was unable to find it with the current ones. If I just missed it, feel
free to reject the pull ;)