Fix several bugs with the STL reader

On windows ifstreams handle data differently depending if the file was opened in binary mode or not. This messed with
the parsing for some files.

Fixed reading a binary file into any other scalar type other than float. Binary STL always contain 32 bit floats, but
the parser depended on ScalarT for how much data should be read, which can lead to false results if e.g. a double
position type is given.