LP-419 avoid gcs config reset

LP-419 xmlconfig: cleanup and remove dead code

LP-419 add settings utilities

provides utilities to initialize, load and merge factory defaults settings

LP-419 main: use new settings utils

LP-419 cleanup QSettings usage throughout GCS

LP-419 config: made IPConnectionPlugin a configurable plugin

inspired from notification plugin next is the serialconnection plugin also made the code more conformant

LP-419 config: apply camel case to IPConnection classes

LP-419 config: made SerialPlugin a configurable plugin

inspired from notification plugin

LP-419 notification: remove unused files

LP-419 dialgadget: convert floats to strings before saving configuration

avoids rounding issues

LP-419 config: merge factory defaults at startup

a simple registry is used to track all configurations ever seen only new configurations (i.e. not in the registry) are added merging only applies to plugin and gadget configurations for now