Usability improvements for including files

When describing a file, bespin-cli requires a CWL File object structure. For example, an array of two files at `['/path/to/file1','/path/to/file2']` requires the following structure:

```
[
{
"class": "File",
"path": "/path/to/file1"
},
{
"class": "File",
"path": "/path/to/file2"
}
]
```

User feedback on this requirement was that

1. The added boilerplate (class, path,) make the important pieces (file name) to identify when comparing lines or files
2. Authoring/editing such files by hand is error prone
3. Copying/pasting the structure is expected and may lead to hard-to-spot errors.

Related to #19