Add named scopes and methods for "status"

Fix #50
Merge branch 'status-as-model-property' of github.com:sarahsemark/suitor into status-as-model-property
Fix a little bug that caused posting page to spew errors.
Set up basic buttons for filtering.
Show original posting link beside edit/delete controls, and refine styling a smidge.
Use date helpers, and use a relative date for deadline (but not date posted.)
Hide empty location brackets.
Move application instructions to its own box below job description.
Put time stuff all on the same line and differentiate deadline icon from posting date.
Show a neater-looking form for application form on posting detail page.
Uppercase and tweak styling of buttons.
Move controls to header and remove unnecessary headers for each side of the page.
Clean up control buttons a smidge.
Only show application form for un-applied jobs if no interview is scheduled.
Show very brief information about interviews.
Only prompt for a follow-up if no interviews exist.
Add ability to archive/unarchive posting directly from detail page.
Add schedule interview form directly to posting detail page.
Change text of archive toggle on toggle, and flash to indicate change.
Rearrange actionable panel on post listings.