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