Add short version of membership description

- Added `membership_desc_short` to database
- House lists displays short version instead of long (helps with narrower screens)
- Use "Full", "Social", "Associate", "RA" instead of "Full Member", "Social Member", etc.
- Also updated how adding members parses the membership type to get the membership type value.
No it isn't, forgot to change that back. The query doesn't work if you pass in table names separately (since sqlalchemy thinks it's a string value, not a table name).