Filter and sort next-transit-times

[jmou]

Present useful times.

• Filter times too soon (train in 1 minute) or too late (train in 1 hour).
• Sort by something like next arrival time
• Maybe try to show results for each line / limit results for each line. For example, if the B52 is 20 minutes away, it might be useful to list it even if there are many trains arriving before it.

[pythagoraswitch]

Currently it is taking the most recent train/bus time excluding the ones less than walk time; filter and sort are implemented in frontend.
The train/bus time also decreases automatically using moment.
Here in this commit -> 8f6b20d

Next to-dos:

• add walk time info for bus stops
• think about which train/bus lines to show first (sort heuristics)