Extract world speed record management into its own class

[ArthurDenture]

I noticed that world speed record management in simworld.cc was pretty self-contained, so I wrote up a patch to move it into its own class. See attached.

It's not a huge win, but it's still a nice small improvement: several dozen lines of code and some member variables are removed from simworld.cc.

[prissi]

Why not, incorporated.

[ArthurDenture]

It looks like you might have forgotten an "svn add" on the two new files...

(On the plus side, http://ec2-54-242-171-11.compute-1.amazonaws.com/jenkins/job/simutrans/ caught this :-).)

[Markohs]

Yep, dataobj/records.* is not on svn, prissi

EDIT: Just uploaded them myself @6695, I hope prissi doesn't mind. I also restored the three slashes comments in the .h world records, that way the comments appear in doxygen, you turned them to two slashes, I hope you don't mind it either.