Add experimental "Modding Mode" setting

[Tkachov]

Overstrike was implemented to install mods exactly how its predecessors do to minimize the possibility of mods working incorrectly.

However, this causes minor inconveniences. Specifically:

1. toc file is compressed with BestCompression level (see DAT1/TOC.cs) in MSMR and MM. This is made for compatibility with suits tool, even though the game can handle other compression levels just fine. Using other level here could make the last step of mods installation much faster.

2. there are 3 different implementations of adding archive entry to the toc, even though any of these should work fine for all the cases.

I suggest adding a "Modding Mode" switch in Settings, and have it "Legacy" and "Experimental" options. In first mode, everything stays the same way it is currently. In second, it uses different compression level, the same archive adding implementation, and maybe does something else differently as well.

The initial value should be selected at random on first launch. This way, experimental mode would get some testing. If it breaks something, users would be able to switch it back to "Legacy" at any time. After some time, when it's obvious that "Experimental" mode doesn't break anything anymore, this setting could be removed with making this new behavior the default and only behavior.