delay loading dependencies until task execution

bower is extremely slow to require(), therefore just loading the bower task
will masssively slow down a grunt build even if the bower task is not executed
in that particular grunt run
adding source argument to layout call in copyAssets function for increased power in the custom layout function
Upgrading bower version to ~1.3.0.
Upgraded traveis node.js version to 0.10 to match bower.
Merge pull request #88 from c089/workaround-slow-bower-require

delay loading dependencies until task execution
Merge pull request #123 from johnkchiu/UpgradeBowerVersion

Upgrading bower version to ~1.3.0 and Node to 0.10
Merge pull request #114 from grawk/devel

increase flexibility in custom layout function
release version 0.4.0