Read and set legacy infoTex

[Google_Frog]

This change means that the legacy infoTex is supported (at least for now?) as a fallback for systems with weak graphics. The change should be extended in the following two ways.

Read whether legacy is active
Lua needs to know which infotex is in use. The interpretation of LOS settings differs between legacy and default so it is important to set the values with this in mind. Currently settings which work well with the default LOS view make the terrain too bright with legacy.

Set whether legacy is active
Sometimes people have graphical issues or slow graphics cards. It would be useful to be able to tell them to switch the legacy just to see whether their bug is fixed. It would be nice to have a command to switch between the infoTex systems although I do not know whether it is feasible. A toggle should at least be added to springsettings.