deprecate dist task, add dist:build task

for now, this is not really visible, since for the next minor versions,
there will be no change, but people should start to know about deprecation
add optional task to create compressed src-packages

Those will be needed for packaging. It can compress node_modules/ and
bower_components/ directories into a single dependencies.tar.gz file and
it compresses an optional dist/source/<pkgName>-<pkgVersion>/ directory
into a source tarball for packaging.
add some copy and dist tasks for source packages

it's now possible to create source packages directly using grunt.
Just use dist:source or dist:dependencies tasks to collect all
sources and dependencies needed for a build in separate tarballs/directories