splat should be lazier in its segment loading

[mkst]

Currently all segments are loaded at startup which means all dependencies are required (e.g. crunch64, libgfxd) - even if the user does not use the segments that use them.

This is caused by the "from . import foo as foo" statements in the __init__.py scripts. These are not required when running splat as a library (the presence of the __init__.py is enough to let python load modules). An open question is whether these statements are required when using splat as a library.

If not, then these __init__.py files can be emptied and we'll get the lazy loading of segments that we want.