Adding support for restoring fixtures between tests

Added helpers/venus-fixture class to handle caching and restoring venus-fixtures between tests
Made some changes to lib/executor, using process.nextTick in place of setTimeout, split out some
callbacks into functions with comments.

Updated .venus/adaptors to include the new venus-fixture helper cache/restoring.
Update .venus/config to include the venus-fixture helper in various configs.
Fixing custom route issue from previous commit.
Merge pull request #187 from rbakr/master

Adding support for restoring fixutres.