Crank up values for tombstone warn and error thresholds.

 - don't try to link against non-existant (and deprecated) libRt
 - strip inotify stuff from FilePusher for MacOS builds
 - Fix istream::read and istream::seekg calls (they won't return NULL on error)

* Bump cpp-driver to 2.0.1
* Create new SensorId header/source that takes over the logic
  previously found in SensorDataStore related to populating
  SensorId structs from MQTT topic strings and serializing
  them into Byte Arrays to be used as Cassandra Row Keys.

* Bumped Cassandra to 2.1.5
* Bumped cpp-driver to 2.0
* Eliminated cassandraBackend in favor of DCDBConnection

In the future, a DCDBConnection handles the low-level connection
to Cassandra. On top of an established DCDBConnection, you can
create a SensorDataStore object which gives you access to raw
sensor readings.

Use the -r option to get raw values instead.

just erronously owerwitten the Makefile in the previous commit. This is the last one edited by Axel.