ebfret.ui.MainWindow: show progress dialog during loading
ebfret.ui.MainWindow: add axis titles
ebfret.ui.MainWindow: refactored clip.* -> crop.*

This is to avoid confusion with between cropping (i.e. considering
data in a window in time) and clipping (i.e. restricting the
signal to a specified interval)
remove_bleaching: fixed regression in e5beae8f065a4f936bf02d0d7712349310f92d34

When auto-removal was selected, the bleaching points were
calculated but not applied.
ebfret.plot.get_bins: ignore inf and nan values
ebfret.ui.MainWindow: new system for clipping outliers

outliers are now not clipped destructively, but rather on demand
(as the cropping is done).
ebfret.ui.MainWindow.refresh: add some safety checks
ebfret.ui.MainWindow.load_data: simplified progress indicator
ebfret.ui.MainWindow: added message box after clip outliers
ebfret.ui.MainWindow: feedback message for remove_photobleaching