Improve build process.
In general, the output is less noisy. Extraneous output from ECJ and DX
is hidden (including the unused import warnings). APKBuilder and DX are
now invoked directly, preventing System.exit() calls. The dex process
has been split into DX Dex and DX Merge. The output messages are now
more useful.
The build preferences have been split off into their own section. A new
setting, Build > "Verbose Output" has been added. When enabled, the
console output will contain much more information about the state of the
build, which can be useful for debugging.