Handle cookies in a more systematic way?

[danielcompton]

The code for validating cookies, cookies on resources, cookie encoding, e.t.c. is in several different locations across several files, and there is some duplication between them. This makes it hard to tell if all cookie attributes and value types are handled in all possible ways of creating them (#296, #297).

I'm not quite sure what it would look like, but it might be good to look at merging the handling of cookies into one unified place so that they can be handled consistently throughout the yada stack?

OTOH, cookie attributes aren't added that frequently, so if it's too difficult then it may not be worth the effort.