Build process improvements.

- Separate out libraries by their purpose, so Netbeans doesn't have
  so much junk on the main classpath.

- Bundle a version of Ivy instead of downloading it.

- Have Ivy remove old versions of libraries instead of just adding
  new ones.

- Write the classpaths themselves to private.properties instead of
  an indirect private.classpath property which shows up weirdly in
  Netbeans.

Change-Id: I33b5fe34cc08d48d1b0e35ee93f21fa62bf8cfdb
Reviewed-on: http://gerrit.dmdirc.com/2705
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager