libknot dependencies cleanup

Divided files from common to common and common-knot, some moved to libknot.

Only those in common are used in libknot and only in .c files. libknot headers are no longer dependent on any headers outside libknot.

See issue #199 (closed)

Reassigned to @jkadlec

Reassigned to @jvcelak

I will resolve this MR as a first thing in the morning. (Well, not really - I will have a breakfast before.)