flights/list: Show comment icon instead of count

This is a bit more intuitive without looking at the table header
README: Fixed bug tracker URL
model/timezone: Fixed copy/paste issue in __repr__() method
js: Make _additional parameter of addFlight() optional
js: Use _additional.color if set in addFlight()
lib/helpers: Implemented color generator
tracking: Use color generator
Merge pull request #169 from Turbo87/trace-colors

Use color generator to define live tracking colors on server side
timeline: Use subqueryload() instead of joinedload()

subqueryload() seems to be much faster in this case due to the
complicated multiple joins.
model/flight: Use deferred column loading pattern for large columns

We usually don't need the timestamps and locations of the whole flight
for each query, so we can only load them if needed (i.e. deferred).
flights: Use subqueryload() instead of joining everything in one huge query
ranking: Fixed 1+n loading of club attribute
Merge pull request #173 from Turbo87/query-optimize

Optimized some SQL queries to reduce server load
flight: Fixed undefer() call
i18n: Updated Dutch translation
i18n: Updated French translation
i18n: Updated Polish translation
i18n: Updated Portuguese translation
i18n: Updated Spanish translation
Merge pull request #174 from Turbo87/i18n

Updated translations