template for application arguments

[alexbruy]

OTB application command line is rebuild when the algorithm is run.
It could be easier if the OTB XML descriptors contained the template of the arguments.
The post processing would be to complete the template with the user arguments.

Todo:

• Add a node cli_args_template to the root of each xml descriptor file. The value of this node is the list of all arguments with a formatable value. All known parameters are already written in the template.

-inp {inp} -inxs {inxs} -out {out} -method bayes -method.bayes.lambda {method.bayes.lambda} -method.bayes.s {method.bayes.s} -ram 512

• Adapt the processAlgorithm function to use the arguments template

Moved from QGIS bugtracker https://issues.qgis.org/issues/14554