Added cmake tests for hiredis

hiredis is the official c client for the redis db. It is
needed to create an Redis IPFIX exorter that can directly write
to the flow-inspector (https://github.com/constcast/flow-inspector)
input queue.
First version of exporter to FlowInspector
Use system wide FindPostgreSQL.cmake

Fixes the search for Postgres libraries by employing the cmake
shipped FindPostgreSQL.cmake file
Move DB specific files to own subdirectory
Renamed IpfixDbReader -> IpfixDbReaderMySQL
Renamed IpfixDbWriter -> IpfixDbWriterMySQL
Added IpfixDbCommon.cpp
Naming changes: Include MySQL in config classes
Configs
Common base class for all SQL database writers
Postgres writer uses common db base class
MySQL uses new base class
Common configuration for SQL-based db writers
Unify SQL database layout for PG and MySQL

Until now we had two different database layouts for MySQL and
Postgres databases. Those two have been incompatible and did
not even encode the same information.
This commit unifies both database schemes to include the same
fields with similar types (e.g. firstSwitched is in milli seconds
for both databases).
Oracle DB Writer now uses common SQL backend

Changes compile currently, but could not yet been tested due to
lack of a working Oracle database
Compile fix when database support is disabled
IpfixFileWriter: Check if directory exists
Bugfix: Proper initialization of collector fields

RAWDIR and DATAFILE writers did not properly initialize all collector
variables on add_collector.
New fields: packetTotalCount and octetTotalCount
Allow the use of bgpSourceAsNumber and bgpDestionationAsNumber

Both fields can now be used in the packetAggregator. However,
their value will be set to 0 for all fields. This was impelemented
to allow to import IPFIX data from vermont into some tools which
require the fields to be present (but ignore the value of the fields)