Fix lines are again redrawn

[nikolai-b]

Sadly this re-introduce double sorting when changing a region.
Fixes #797

[Robinlovelace]

Confirmed issue demonstrated below on master.

[Robinlovelace]

Fix demonstrated after merging #798

[Robinlovelace]

Tested with straight lines, cannot see any unintended consequences. Definitely fixes #797.

[Robinlovelace]

Quick check-in question: can you think of any unintended consequences of this @nikolai-b or @usr110 ? I've had a look over the code and quick test and it seems fine but thought it worth checking. Thanks!

[nikolai-b]

@Robinlovelace thank you for the quick test but I just wasn't happy that we were re-sorting the lines twice when changing region. I've fixed this in 440fe02 and noticed that we were also re-drawing zones af9c840
If your still happy I'll merge.

[Robinlovelace]

I think this is a definite improvement although don't have a very strong understanding of the this part of the code.

@nikolai-b when you say we're re-drawing the zones, could that also be slowing down the initial load? If so I'd suggest merging this into master and production and then working on that in a separate issue to keep things moving.

[usr110]

Great work @nikolai-b

Just testing it and found an interesting phenomena. For london, specifically, if you move about the map - while the top lines remain as they are, they are redrawn. A lot of changes have been recently made, so I am not sure if it's a known issue or not.

Edit:
Just for comparison, I didn't find the same issue on the live-server.

Noticed that the production branch too got recently updated so can't really use it for comparison, but if my memory serves me right, this didn't use to happen.

[usr110]

The lines are not redrawn - sorry about it @nikolai-b

Two things confused me:

1. The plotting message saying that they are redrawn. I know they're used for local testing, but with messages like Plotting top 30 straight_lines took for straight_lines is slightly confusing.
2. The loading circle - which is a minor issue.

thanks!