Rename and move Builder descriptor classes

* Moved Builderxxx from guicommon to fluidx namespace
* Renamed Builderxxx to AdvancedxxxDescriptor
* Moved GeneratorSignature and FunctionSignatureRegistry from guicommon to ware namespace
Change management of Observers signatures and check

* Created an ObserverSignatureRegistry class to store Observers plugin signatures
* Created a WaresHelper class to perform checks on Monitoring plugin files
Move Function plugins checking to WaresHelper
Refactor FunctionSignatureRegistry

* Made FunctionSignatureRegistry update himself in constructor, avoiding some explicit updates
* Removed FunctionSignatureRegistrySub class, thaht was used for tests but is no more useful
* Used of built-in example functions as default functions for FunctionSignatureRegistry test cases
Change return parameter of WaresHelper check functions

* Monitoring and Model plugins checking now fill a list of missing IDs, instead of a textual list
Refactor relations management in AdvancedDomainDesc

* Added check of Unit relations when adding a Unit to the domain
* Made const the access to Unit relations to forbid direct modifications
* Added functions to add or remove a relation between two Units, and clear all relations of a Unit with others