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
templates/upload/result: use vertical tabs for flight list

Import bootstrap-vertical-tabs.css from
https://github.com/dbtek/bootstrap-vertical-tabs
with some minor modifications for small layouts.
templates/upload/result: show barogram of uploaded flights
baro.js: pass additional options to flot
Fork flot-selection plugin
Rename jquery.flot.selection.js to jquery.flot.flight-upload.js
jquery.flot.flight-upload.js: adjust coding style
jquery.flot.flight-upload.js: remove unnecessary y-range stuff
flight-upload.js: default selection color is dark gray
flight-upload.js: invert selection
flight-upload.js: every selection is sane.
flight-upload.js: change selection only when dragging the takeoff/landing markers
flight-upload.js: change cursor style if cursor is over a marker
flight-upload: don't stroke around gray area, show single lines only
flight-upload: always use first x-axis
flight-upload.js: rename first and second position to takeoff and landing

Prepare keeping them sorted and adding a release time marker.