Create a CWL validator

[ivanbatic]

The validator should be relatively optimal in terms of feedback speed. The errors are to be reported to the user in the Ace editor.

[mayacoda]

For now, errors will be displayed in an errors console. In the future, we'll add inline validation inside the code editor.

[mayacoda]

Also, validation will work kind of like this:

• JSON schema validation as a first line of defense. This type of validation will reveal obvious errors, ones that make the description not CWL.
• After a tool has passed JSON schema validation, that means it's the proper format to be loaded into the model. The model will then return semantic validation errors, if any.
• If the file is changed via text mode, tool goes through JSON schema validation again and is reloaded into the model
• If the tool is changed via GUI mode, the model handles realtime semantic validation and does not allow for an invalid CWL tool to be created.

[mayacoda]

Closing in favor of discussion on https://github.com/rabix/cwl-ts