views.upload: Pass upload status as enum to template

Make it easier to reuse the status text messages.
views.upload: split update method

Prepare updating single flight per ajax request
macros/form.jinja: add macro to render pure fields without label
frontend.views.upload: finally redirect to a list of uploaded flights
templates/upload/result.jinja: reimplement using WTForms
lib.paginate: rename file to table_tools.py
views.ranking: add basic table sorter
templates/ranking/*.jinja: add sorting macro
templates/ranking/*.jinja: add pagination status to table sorter
views.ranking: sort by rank
Merge branch 'wtf_upload'