Tokenizer for quoted argument strings
Filtered Reader for replacing tokens
Support blank replacement values

* flag for replaceDataReferences, and replaceTokensInFile/Script/Stream
Use quoted string tokenizer

* update tests
* quote blank strings when joining
Use blank replacement value for missing context vars
Support blank input values for options
Tokens must have all chars within a certain set
Update UI text for Option.required
Update docs with for changed behavior

* blank values allowed
* default values used
Show required warning if blank is preset
Add button to use default value for option
Merge pull request #440 from gschueler/issues/352-blank-options

Issues/352 blank options for #352