Add missing configuration arguments and enforce logical consistency of configuration.

[carlwilson]

The veraPDFTaskConfig class provides a single entry point for configuring an invocation of the veraPDF software. The class is based on the options described in section 6 of the Functional Specification document, "Functionality and interfaces".

There are two issues combined here:

• Not all arguments described in the functional specification are present.
• Some combination or arguments are inadmissible / logically inconsistent.

Reading the scenarios in the specification should highlight config parameters that aren't implemented yet, these should be added.

The specification highlights some other requirements, e.g. if the -pdfa argument isn't present the -profile argument MUST be. Some basic boundary condition checks are present, e.g. legal values for verbosity and stoperrors. These are implemented as Guava Preconditions.

The task is to read the specification and add arguments / preconditions as required. This may highlight inconsistencies in the specification. If the answer is obvious then change the specification and adopt the "common sense" answer. Where there are questions simply flag them in the code / specification for clarification.