passing metadata_urls should be done through proper url query parameters

[marcellmars]

https://github.com/marcellmars/letssharebooks/blob/master/server_side/libraries/static/libraries.js#L89 and related: https://github.com/marcellmars/letssharebooks/blob/master/calibreletssharebooks/main.py#L1121

should pass the url query parameters in a more robust way. e.g. dictionary: opf, cover, format(s)...

[marcellmars]

lines in main.py:

 def http_import(self, r):
    if request_data[:7] != "/?urls=":
    ..
    req_seq = request_data.split('__,__')