First pass at proper POMs for building and packaging things.

The gdx-tools artifact even properly bundles the various extra jars into
itself. The only thing still missing is a POM to create the gdx-platform
artifacts, which I'll tackle next.
Name the parent gdx-parent.

Everything else is gdx-something, so it's weird that parent is bare.
Maven wiring to build natives jars.

This currently downloads the jars from the build server. It may be possible to
have Maven actually do the native builds, but that seems like perhaps more
trouble than it's worth.
Allow running particle editor via Maven.

From the top-level directory:

mvn -f extensions/gdx-tools/pom.xml test -Pparticles
Merge branch 'poms' of https://github.com/samskivert/libgdx into maven
Merge branch 'poms' of https://github.com/samskivert/libgdx into maven
manually merged changes to platform/pom.xml by Michael
Merge branch 'master' into maven
Merge branch 'maven' of https://github.com/libgdx/libgdx into maven
Merge branch 'master' into maven
Merge branch 'master' into maven
fixed groupId in poms
Add alphaTest
Added ObjectFloatMap.

Moar mapz!
Added getItemHeight.
Added updateVisualScroll for setting scroll position without animating.
Fixed size bug in Array constructor.

Yikes!
Rewrote SelectBox list to use ScrollPane and List.

Now SelectBox scroll if there are too many items to fit onscreen.
Merge remote-tracking branch 'origin/master'
Fixed javadoc warnings.

So fresh and so clean, clean.