minor draft improvements related to #189

add last saved timestamp to drafts and display this timestamp as date in postbox's drafts list
replace usage of need type strings such as "SUPPLY" etc. with won.WON variables like won.WON.BasicNeedTypeSupply etc., so that the need type icon can be displayed by the same function for both need and draft
add sorting by title and date for postbox's drafts
show most recent drafts in "new post" submenu
Merge remote-tracking branch 'origin/1.0-bugfix' into 1.0-bugfix