master: Refactor 'struct chunks'

Remove unnecessary typedefs, simplify lots of state updation code.
master: Support chunk state update notifications

Reloading chunkserver configuration can transition some chunks between
the VALID and TDVALID states. The chunkserver notifies us about such
event with the LIZ_CSTOMA_CHUNK_NEW message.

Make master update chunk "todel" state upon reception of such message.

Also, try to handle some unexpected updates that can theoretically
occur due to some bugs.
master: Fix versions of temporary throwaway chunks

When chunkserver reports a chunk with ID unknown to master, master
creates a chunk with this ID in its data structures and lets chunk
jobs take care of removing it (as an unused chunk).

These temporary chunks were getting wrong IDs when copies reported
by the chunkservers were marked "to delete". This commit fixes it.