Handle 'default' values and "minOccurs=0" in CWL from WPS-1

[fmigneault]

ref #12, #11

CWL: how to set default values
(1) https://www.biostars.org/p/221531/

Common Workflow Language User Guide - Essential Input Parameters
(2) https://www.commonwl.org/user_guide/03-input/

More details here:
(3) https://www.biostars.org/p/286135/
"default" generates "type": ["null", <other-real-type>] and "<type>?" is a shorthand for this same type definition

todo

• add test when "default" is present for a LiteralData value
• add test when "default" is present for a "File" reference
• add test when "minOccurs"=0 is present for a LiteralData value ("default" as "null")
• add test when "minOccurs"=0 is present for a "File" reference ("default" as "null")
• add test when "maxOccurs">1 is present for a LiteralData value (coverted to "type": "array")
• add test when "maxOccurs">1 is present for a "File" reference (coverted to "type": "array")
• add test for shorthand "<type>?" by itself, and with every combination of above cases, as well as with multiple cases combined (validate all situations are handled correctly)
• add test when "minOccurs">1, type should be converted to array automatically, maxOccurs should be updated accordingly to array methods as above.

extra

• add test when "allowedValues" is present with a list of allowed values, which should resolve as enum type (relates to AllowedValues missing from process descriptions #41)
• add test when "allowedValues" + ("default" and/or "minOccurs"=0 and/or "maxOccurs">1) are present, to validate that everything still resolves properly [see ref (3) for more details about potential failure for "enum?"]

edit
Could introduce new CWL methods to define int/float Range or string AllowedAalues (similar to enum) following outcome of common-workflow-language/common-workflow-language#764

For Workflows, see developments related to following spec:

• FormalParameter fields BioSchemas/specifications#452