Remove text reference to "Full weekend pass"

Changes the index page to say "Membership for Anthrocon" instead of
"Full weekend pass."
Pre-reg form text changes

Changes "con" to "convention," and adds a text notice about dealer
registration.
Add custom price-change text

Adds custom text to describe a single price change. Requires a new date
setting called first_price_bump.
Merge pull request #745 from magfest/change_text

Custom AnthroCon text changes