lib: Move space command classes into a distinct translation unit.

This affects the following classes:
* SpaceCommandFormatException
* MissingCommandParameterException
* IllegalCommandParameterException
* SpaceCommand
* SpaceCommandSerializer
* TextSpaceCommandSerializer
lib: Introduce a util translation unit for utility classes and methods.
lib: added hex2int from i2cmethods to utilities.
lib: added int2hex from i2cmethods to utilities.
lib: restructured util/int2hex

use a distinct function to calculate the hex width
lib: added retrieveHexParameter from i2cmethods to utilities.
I3C Client: Use xmppsc/util.h for utility methods
I3C CLI: Use xmppsc/util.h for utility methods
I3C CLI: Removed i3c_client dependency.
Merge pull request #32 from penguineer/restructure

Restructuring which mainly leads to a better decoupling of software components.
(I3C CLI no longer depends on I3C Client)