openlayers: Moved images into "img" folder

This is the original name of the folder in the openlayers project
openlayers: Removed unused styles from CSS file
openlayers: Added ol-ZoomControl.css file
openlayers: Improved zoom control styling
openlayers: Use id instead of class for layer switcher elements

This resolves a conflict with the global .box class and the layer switcher
openlayers: Improved layer switcher control styling
config/default: Set ASSETS_DEBUG to False
openlayers: Added checkmarks to layer switcher styling
openlayers: Moved checkmark to the lower right corner
requirements: Pin "werkzeug" package to v0.8.3

The current stable version 0.9 is incompatible with flask 0.9
Merge pull request #86 from Turbo87/werkzeug

requirements: Pin "werkzeug" package to v0.8.3
Merge pull request #85 from Turbo87/map-css

Adjusted map control styling
views.upload: use async task for in-depth reanalysis of uploaded flights
views.flights: add analyse_all method to reanalyse all flights

Used for debugging atm, should be removed later (there's the
analysis.py script for that purpose).
Merge branch 'master' of github.com:skylines-project/skylines into celery