Completion of simulation monitoring with observers

* Removed <output> section from FluidX format
* Introduced <monitoring> section in FluidX format
* Renamed ObserversListXxx classes to MonitoringXxx classes (instance
  and descriptor)
* Updated tests and tests datasets  

(closes #18)
Change Builder descriptors constructor

Builder descriptors are now directly initialized with fluidx descriptor.
Add model check in BuilderModel constructor
Bug fix in Builder Model structure display
Bug fix in Builder Simulation Run display
Bug fix when adding a Unit

* Added default input data when adding a new Unit to the domain
* Added Domain modules updates on initialization
Merge pull request #55 from alibres/builder-with-descriptors

Bug fixes in Builder with descriptors
Use the model descriptor to write fluidx
Use the domain descriptor to write fluidx
Write <model> tag in fluidx even if model is empty

* Write empty <model> section in fluidx file if model descriptor is empty
* Cleaned code
Use the datastore descriptor to write fluidx

* Used the datastore descriptor to write fluidx file(s)
* Written an empty <run> section if run descriptor isn't filled
* Cleaned code
Monitoring section is now written to file(s)

* Added writing of <monitoring> section in fluidx file(s)
* Added check of <monitoring> section in FluidXDescriptor tests (Monitoring is now part of all test input dataset, specific "with observers" test has been removed)
* Added global check of written files
* Fixed missing writing of run <simid> section
* Renamed fluidx test dataset from FluidXReader to FluidXDescriptor
Reactivate save function in Builder
Fix bug when closing the Model structure tab

(closes #50)
Merge branch 'fix-50' of https://github.com/alibres/openfluid into alibres-fix-50
Refactoring of wares initialization and introduction of datastore in
wares

* Modified initialization hierarchy in wares
* Added datastore link in wares for future access during simulations
* Modified openfluid-engine strings

(references #8)