flag user privacy status

[dchud]

• add an "is_private" column
• check user_timeline fetches and update as appropriate
• use column value to limit browsing
• use column value to limit future user_timeline calls
• limit downloads

[dchud]

consider aligning rights with UserSets; perhaps only the user(s) assigned to a TwitterUserSet would have the right to see / browse / export users marked private.

[lwrubel]

See TAGS spreadsheet with tweets from @WoodlandsVB food truck: https://docs.google.com/spreadsheet/ccc?key=0Ak1GYS9L91xodFFvYk1fU2Z6NEZtcU1CVWc0VUtvTmc&usp=sharing