Correct the pmg scraper's fetch-to-limit option help text

It should refer to a seen report, not a seen question
Carry on to other committees after encountering a seen report

This fixes the bug where the scraper would stop completely if it
came across a seen report instead of progressing to the next
committee.
Only log in to the PMG site when scraping premium committees

PMG have requested this to reduce load on their server.
Merge commit 'bb6a2afa18fa858f7'

This merges in Geoff Kilpin's changes from the pmg-scraper-updates
branch.
Remove an unnecessary 'pass'
Remove unnecessary uses of str(); this is done anyway
Change whitespce to be as PEP 8 prefers
A small refactoring