Removed Z-up function from Client/Center()

Turns out this was allowing mecha to travel semi-unrestricted upwards
through z-levels, including to Central Command and the Away Mission.
Another tiny change to IRC nudge.

HTML entities are now unescaped so that they show up correctly on IRC.

Signed-off-by: Mloc-Argent <colmohici@gmail.com>
Merge pull request #3448 from TwistedAkai/master

Removed Z-up function from Client/Center()
Merge pull request #3449 from Mloc/nudge2

Another tiny change to IRC nudge.
Fix for #3450. Also, stuff.
Tape is not a lattice.
Merge pull request #3453 from Segrain/master

Bugfixes.
Merge branch 'master' of https://github.com/Baystation12/Baystation12
Merge pull request #3457 from Zuhayr/feature

Feature