Changed most of the imports to parts.

Also moved lib/server to lib/src/server since it's already exposed as part anyway.
Adapted the tests to run properly

dart_analyzer resolves parts automatically so there's no need to call it for every .dart file

If called on every dart file it crashes now, since the imports aren't properly resolved.
Merge pull request #14 from enyo/import-part

Refactored the way the files are included.