Seperate out the key interfaces/data into a seperate @kangojs/common package

[ben-ryder]

Package: kangojs/common

Describe your improvement
Separate out common interfaces/data into a common package:

• Error identifiers
• HTTP status codes

Is your suggestion related to any problems?
A front end package requiring the error identifiers shouldn't need to pull in the entire core package, even if the client will sort tree shaking itself.

Right now a client also need to install express & cookie-parser types to which it shouldn't need

Additional context
n/a