rename model: Roster -> DayRoster
model/duty: add classmethod to find DayRoster by date
model/duty: bugfix
templates/duty/list:edit/add <table>s for debugging
views/dutys: change view to new model with dayRoster as parentclass instead of Duty
templates/dutys/list: add variable <tabel>frame for dutys without content
templates/navs: remove navlink
templates/duty/list: add navlink