refactoring: ActorDefault -> ActorComponent

ActorDefault is now ActorComponent according the naming convention.
refactoring: add a support for PowerUnit description

PowerUnit was extended for adding a short name and a long name which can be used for the reporting.
refactoring: Channels externalization for the module package.

For the coding convention, the code of SensorChannel and PowerChannel was separated in different files.
refactoring: Move methods from Procfs sensors inside the LinuxHelper.

Move the methods useful to read the cpu time inside the LinuxHelper.

refactoring: Improve the method encapsulation.

typo:  Fix a typo in @author tag.