Change module names 'plates' to 'lithosphere'

[MFraters]

Currently the continental plate and oceanic plate do not models what is defined as a plate, but what they model is better described as a type of lithosphere. I think it would make sense to rename them accordingly. The downsides is that this this a name change a very core part which will require to change nearly all input files, and secondly it make the name even longer.

I don't think the first downside is a major problem yet because of the clear versioning and the world builder being in a beta status. The second issue might be overcome with a shortened name for lithosphere, but I am doubting whether that is the correct approach and whether the problem is large enough to require it to actually shorting lithosphere to for example litho. The downside of shortening is also that it become less clear.

[MFraters]

After several discussions, I decided to keep it as is for the foreseeable future.