model: add missing indexes

They both speed up some long-running queries.
model.flight: speed up elevations query

Remove 'elevations != None' check in SQL query but check it in the
following flat loop. That saves 1/4 to 1/3 of the SQL running time.

Using a CTE instead of a subquery is a more explicit way to tell the
postgres planner that this part of the query is constant.
notifications/timeline: fix privacy_level filter
flightpath: check for output length before adding elevations

This should fix #288
commands.import_.srtm: add option to import local files
model.flight: speed up elevations query even more
flight.js: remove unneccessary .show() and .hide() when adding/removing a plane marker
flight.js: don't recreate the plane icons on every update
flight.js: clone point for plane icon

Otherwise moving the plane icon changes the linestring itself.
flight.js: use ol.LonLat instead of ol.Point for transformation

LonLat is more lightweight...
setup.py: update Flask-WTF to 0.9.5

Fixes a bug with the new released WTForms 2.0 which doesn't
work with Flask-WTF 0.9.x
templates/tracking/info: update webserver URL

Fixes #318
livetrack24: store terrain elevation of fix

Fixes #269
flight.js: create a new point for the plane marker, don't clone it.

Cloning clones the parent, too, which has unpleasent side effects
when moving the points.
i18n: Fix german translation
Merge pull request #322 from fb/master

i18n: Fix german translation
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