Add order by ascent count function to line list

[dorthrithil]

After changing the ascent count to a hybrid property, it is not trivial anymore to order by ascent counts. For the ORM to resolve this, we need a hybrid property expression and this has to compute the ascent count for every line there is for ordering to work - which is performing badly.

To solve it, I see no other way then adding back the ascent count column and incrementing and decrementing it in the ascent routes. This will not collide with the secret spot issues we had (wrong ascent counts if you're not logged in and can't see secret ascents) as secret lines can only be seen by logged in users - in contrary to public crags with secret lines.

Also an idea would be to change back to the increment / decrement approach again completely and keep two props: ascent count and secret ascent counts. This would speed up the routes again and be consistent across all entities.