adds work package i18n
adds an early version of having a unified new action/view for issues/planning_elements
restructures the way the work_package form is rendered
enables status for issues
provides priorities for the view
reenables switching trackers
reenables autocomplete on parent relation
keeps attributes when changing the tracker

This is not yet fully functional by far as the method relies on safe_attributes which does not know some of the new fields, e.g. responsible
fixes start/due_date calendars
moves copying of an issue into the model
returns empty allowed_status if the issue currently has none
no longer warns against a lazy spec implementation if AnonymousUser is set
harmonizes work_package building across issues/pe
initial implementation of work_package_controller#create
rerenders new when error occurs on work_package#create
fixes omission preventing rendering of a version link
table column end_date was renamed to due_date
assigns planning element attributes on work_package creation
i18n for work_packages
fixes autocompleter for issue parent_id