Refactor blend mask snapshots

fix to importer

next iteration of AO

added blur to SSAO

initial AO withou blur

undo redo of blend mask (#7)

Further minor refactorings

Minor renames in textureHistory

Rename maxNumTiles into numTiles

Remove textureHistory everywhere where it's not necessary; Move textureHistory creation to the baker pass;

Minor changes to how strings are treated for BKRCommand::SelectOutputCommand

Add a command to select files in baker; Move baker commands to BKRCommand namespace;

Add toggle smooth normal command; Convert BakerPass to use std::shared_ptr;

Fix a lot of bugs related to undo-redo of painted blend mask

undo redo of blend mask