improve(express): update express to version 4

Express 4 has a few backwards compatibility breakages.

1. Express does not depend on Connect anymore, all bundled middlewares are not independent.
2. Express router now works slightly differently.

Merge with care, I haven't tested it too thoroughly.
I've tested a few static pages, logged in, completed some tasks, changed my profile settings, all seemed to work. But it's a big change, so beware.