[UNTESTED] Call dx from Maven profile

Convert the dx calls from build.sh to equivalent exec calls in Maven
deploy profile.

While this pull request takes into account differences between Windows and *nix,
it was only tested on Windows, and the resulting binaries have not been
tested at all!

In addition, I was not able to pass individual .class file names to dx
without getting a "class name does not match path" error, so I changed it
to copy all required classes into a temp directory and call dx from there.

I also changed the cross-project paths to refer to the respective Maven
classpath, so in case you do an individual project build, the library
dependencies are taken from the Maven repository instead of taking them
from the target/ directory of the projects directly.

See #1708