nav mesh fixes for maps

[DarkStrike]

Hello. I've noticed for a while now that there's a problem with the navigation mesh on custom maps, causing bots to get stuck in doors and only move along one path. This tilts the balance in favor of one team or the other (mostly on de_overpass, where the T team 99% of the time only goes to the B site).

Today, I fixed these issues by manually editing the nav files.

de_vegas_lite:
Bots at CT spawn no longer get stuck behind doors + paths outside the map have been removed.

de_overpass:
Bots from T spawn can now climb up stairs and descend ladders.

de_mirage:
Bots from T spawn can jump onto a box and easily jump to B site, can climb through the second passage near the window and jump to mid, and are also better at entering from mid on parapet

General:
Bots jump less on steps + minor fixes

Not everything has been fixed, but I think it's improved.

Demo:
https://youtu.be/IIpqMjaD-WY