refactor common header/cookie params to cut down copy-paste

[wrschneider]

This takes advantage of the Python ** operator for keyword arg expansion from a dict so you don't have to repeat the same headers=xxx, cookies=xxx, verify=xxx everywhere

[drzamich]

Thank you @wrschneider for your contribution. Right now we are working on a major codebase update, therefore we cannot accept this PR directly, as it would create a lot of conflicts. We will however take your remark into consideration.