Changes

CellML Annotation view: fixed a class member access problem.
Indeed, we were trying to call 
CellmlAnnotationViewCellmlElementItem::type() on our model’s invisible 
root item, which obviously cannot work, even though it used to be
‘fine’ until now…?!
 (commit: f68b4e7)

Some minor cleaning up.
 (commit: f844538)

Moved SimulationExperimentViewSimulationWidget::FileType to
SimulationExperimentViewSimulation::FileType.
 (commit: c0aa60c)

Some minor cleaning up.
 (commit: 85f218d)

Some minor cleaning up.
 (commit: f5c441e)

CellML support: added a method to directly check for a CellML file's
validity.
 (commit: 15e80ae)

Some minor cleaning up.
 (commit: e78cc96)

COMBINE support: now have methods to check that it is supported and to
retrieve its corresponding SED-ML file.
 (commit: ce0df3f)

SED-ML support: allow the creation of a SED-ML with the file name of
its owner.
This will come handy later on when we can retrieve the corresponding 
CellML file of a SED-ML file.
 (commit: 57721e2)

SED-ML support: can now validate a SED-ML file directly.
This is in contrast with before where we could only validate some file 
contents.
 (commit: 27d911e)

Some minor cleaning up.
 (commit: 60e208f)

Moved
SimulationExperimentViewSimulationWidget::sedmlAlgorithmSupported() to
SedmlFile::algorithmSupported().
 (commit: f16d5ec)

SED-ML support: now have methods to check that it is supported and to
retrieve its corresponding CellML file.
This has basically meant moving 
SimulationExperimentViewSimulationWidget::sedmlFileSupported() to 
SedmlFile::isSupported() and 
SimulationExperimentViewSimulationWidget::retrieveCellmlFile() to 
SedmlFile::cellmlFile().
 (commit: c39b0d5)

Some minor cleaning up.
 (commit: d05af71)

Simulation Experiment view: prevent a potential problem with filters
when exporting a simulation to SED-ML or a COMBINE archive.
 (commit: 2376e25)