Fix password change form

form_for(model) uses PUT, but form_tag uses POST
Add test for password changing + email
Don't check feed_day.pubdate in arxiv_update

This is confusing in cases where we're updating when our
local day is ahead of the arXiv's. Since update_metadata
is now idempotent, the result should be the same.
user_edit_path -> settings_path in test
Update README with dev setup instructions