[Feature] Obtain process 'abstract' from CWL 'doc' field

[fmigneault]

CWL offers the doc field for every I/O as well as top level for the whole tool documentation.
We should use these fields when corresponding abstract is not provided for WPS elements.

similar to #31, but for whole process metadata as well as per-I/O

It is to be noted that [cwl doc ref]

Any doc field may be an array of strings in addition to the previously allowed single string.

Therefore, if doc is given as list of string, it will have to be handled and merged using "\n".join(<strings>). Probably we can reuse

weaver/weaver/utils.py

Line 812 in 9917dcc

def clean_json_text_body(body):