improved Point == and !=
bdf2 pointer changed, progress
weakform reuse progress
progress
bdf2 refactored
control of matrix recalculation implemented.
Works for higher order bdf.
For fixed step 2x speedup (probably should be improved), for adaptive cca 20% (due to keeping one weakform and calling set_ext on it)
times may differ for other examples
new calculation chack introduced. All checks(invoking QMessageBox) cause fail! Maybe due to threads.