Implement More Linting

- [ ] Certain parameters types require default values, these should be validated.
- [ ] Check test data files exist.
- [ ] Check tests test something (`raise Exception( "Test output defines nothing to check (e.g. must have a 'file' check against, assertions to check, metadata or md5 tests, etc...)")`)
- [ ] Ensure supplied test parameters reference inputs.
- [x] Compile RST in Help ensure compiles cleanly.
- [ ] Check datatypes (requires a target Galaxy and tool shed) https://github.com/galaxyproject/planemo/issues/678
- [ ] Flag a warning if `force_history_refresh` is enabled. https://github.com/galaxyproject/tools-iuc/pull/80#discussion_r27023809

Start by locating the existing linting entry points and validation checks in Planemo, then review how tool tests and test data are represented. Work through the unchecked items individually and use the project's existing test and lint commands to verify each validation; done means the requested checks are implemented and the full test suite passes.

Written by the indexing model from the issue text.