Change complete structure of the „Subject Public Key Info“(spki) ADT

These changes were made to reduce the coupling and allow implementation switching without modifying the
code.

- Add a interface „spkitable.h“
- Add new types to store the (ASN, SKI, Subject Public Key Info).
	There are now two representations, one for internal use (key_entry) and
	one for external use (spki_record).

*The old implementation is still there but isnt used anymore. (rtrlib/keys)
*There is currently a SEGFAULT in the tommy_hashlin_insert function.