Made it so we always show what slicing engine we are using in settings
Made it so when we switch to MatterSlice for dual extrusion we reload the display correctly
Put in a clear history button on settings
STLs can now stop loading during most of the load operations (only sort verts cannot)
Changed the signature on report progress ratio to make it clearer.
Made mesh viewer handle better load stoping.
Refactored a bunch of file names and other data.
The QueueData and the LibraryData are practically the same class and shoud
be shared as we move the QueueData into the data base.