Pass deployed library state to dapp test

[namrapatel]

Description

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 — @MrChico

• Write a new little dapp helper script which is the dapp --library-addresses above
• Make dapp build and dapp --make-library-state use this helper script instead
• 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

Closes #881

Checklist

• tested locally
• added automated tests
• updated the docs
• updated the changelog