Add isTemplate parameter to readSensorBase() and readSensorGroup() to reduce debug output for templates

- Auto-publish has been split in two parts: construction of the
sensor names is performed within the Configurators, whereas the MQTT
messages are sent from the MQTTPusher
- This way, sensors always have the correct names upon plugin reloads
- Will make switching to textual MQTT topics easier

- Now sensors can be configured to be automatically written to files
(sink param)
- A per-sensor subsampling feature has also been added, allowing to
decimate the frequency of readings sent to MQTT compared to those that
have been sampled
- Also fixed a bug in MQTTpusher that caused reduced message rates

- Fixed template management when configuring ProcFS and Tester instances:
sensors are not inherited from the template, preventing inconsistencies
- Fixed a bug that caused the "global" config block to be not recognized
anymore in plugins

- Sensors now support a "delta" field in config files. If set to "on",
differences between successive readings instead of the raw values will
be stored
- Default is "off"
- This option should only be applied to monotonic sensors
- Can be applied to perfevents as well

- Now all sensors across all plugins adopt the naming convention
cpu<CPUid>.<sensorName>, if CPU-related, or just <sensorname> otherwise
- Code to parse cpu sets used both in Perfevent and ProcFS plugins
moved up in ConfiguratorTemplate
- Misc code to format MQTT parts also moved up in ConfiguratorTemplate

- This commit reflects changes made in the master branch and should
make the eventual merge less painful

- Now all sensors across all plugins adopt the naming convention
cpu<CPUid>.<sensorName>, if CPU-related, or just <sensorname> otherwise
- Code to parse cpu sets used both in Perfevent and ProcFS plugins
moved up in ConfiguratorTemplate
- Misc code to format MQTT parts also moved up in ConfiguratorTemplate

This is the first batch of changes, more to come