Allow for variable peel times

Big, solid models have large layer surface areas that require a slower peel time to gently overcome the vacuum at the model-PDMS interface. The currently available default peel time is fine for small models but too quick for big, solid models and places tremendous forces on big models and their supports during the peel. In addition to damaging the model, the concussion of breaking the vacuum during fast peels on big, solid models probably affects laser alignment over time and explains why so many people have ongoing problems with failed prints after the first few attempts. (Formlabs tried to print a large object submitted by me and experienced the same model breakage and errors that I have been experiencing. See attached photos.) Preform calculates the area for polymerization on each layer prior to turning on the laser. It seems to me that Preform should predict in advance which layers will encompass a large area and produce a strong vacuum requiring a slower peel immediately after.