Make dev/common dependencies global

[andrewgordstewart]

Dev dependencies (eg. truffle) should be global, so that we're using the same version of truffle across packages.

Some other dependencies, such as web3, should probably also be global, so that we're using the same web3 everywhere.

[andrewgordstewart]

Might want to be part of #30, which upgrades truffle in fmg-simple-adjudicator