EIT signature cache

[Stuart Auchterlonie]

Here is the EIT signature caching patch.

This creates a signature for an event and keeps track of this signature and compares it against incoming EIT data.

Events without a cached signature are added to the DB. Events with updated signature are added to the DB. Events that are unchanged are ignored.

Event signatures are stored in a QMap, with 64 bits available for both key & signature.

Currently the key is (transportid, serviceid, eventid) with the signature (tableid, version, chksum).

Currently the chksum is unused, but can easily be added if necessary.

[Stuart Auchterlonie]

EIT signature caching patch

[danielk]

(In [9228]) References #1035 and closes #1427, by applying patch from #1427.

This implements an event signature cache, so that we avoid processing an event again during any one EIT scan.

This should lower the memory requirements and CPU load of the EIT Scan somewhat.