Fix jetty runner by adding asm dependency.

The dependency "asm" % "asm" % "3.3.1" is missing, which causes jetty
to fail to start under the geotrellis-jetty or dependent projects.
This commit adds the dependency to the jetty project.
Add configuration for demo resource package.

The demo project isn't currently configured to load Jersey
resources from the "demo" package where the services in the
demo subproject live.  This commit just restores the one line
config:

geotrellis.rest-package = "demo"
Merge pull request #688 from joshmarcus/add_demo_config

Add configuration for demo resource package.
Merge pull request #686 from joshmarcus/fix_jetty_deps

Fix jetty runner by adding asm dependency.