Change MIX files to be loaded from a single list

[ZivDero]

Changes mix files to be loaded from one list with the value controlling if they are required or optional. Meant to help merge the 2 TS branches.

Config for YR:

0=langmd.mix,1
1=language.mix,1
2=$EXPANDMD
3=ra2md.mix,1
4=ra2.mix,1
5=cachemd.mix,1
6=cache.mix,1
7=localmd.mix,1
8=local.mix,1
9=$RA2ECACHE
10=$RA2ELOCAL
11=conqmd.mix,1
12=genermd.mix,1
13=generic.mix,1
14=isogenmd.mix,1
15=isogen.mix,1
16=conquer.mix,1
17=marble.mix,0		; borrowed from Final Alert 2

[Rampastring]

This looks somehow heavy to parse for my eyes...

I'd prefer something like

0=landmd.mix,1
1=languagemd.mix,1
2=$EXPANDMD
; ...

Where the optional number after the name would denote whether it's required

Maybe even the current style would be good enough if the "required" status could be specified with a boolean or a number though

langmd.mix=1
language.mix=1
$EXPANDMD=0

[Rampastring]

Make this part into its own function, such as LoadMixFiles, to keep the general ReadConfig function flow clean. I liked how it was originally just a few DoForEveryValueInSection calls.

It could even be LoadMixFile(string entry) so it could be called with iniFile.DoForEveryValueInSection.