convience methods for skipping library deployment

deploying libraries can take a long time. One can easily skip this stage if we make it possible to save the deployed library state and pass it to dapp test:

1. Write a new little dapp helper script which is the dapp --library-addresses above
2. Make dapp build and dapp --make-library-state use this helper script instead
3. Allow a flag --state to be passed to dapp test (probably along with env var DAPP_TEST_STATE), which would override the default behaviour of the library deployment that happens automatically

Now if you want to cache this annoying 45s process that happens everytime, you would put:

export DAPP_LIBRARIES=$(dapp --library-addresses)
export DAPP_TEST_STATE=$(dapp --make-library-state)

in your makefile