changes_for_website

#Major changes
- Added copy/paste embryo feature. Now can also copy embryo objects between molecule objects.
- Added copy/paste background feature. Now can also copy background objects between molecule objects.



- Fixed Bug where analyze all datasets resulted in error if dataset had no background dataset.
- Fixed some unnecessary print outs.
- Fixed save dialog to show .pk files and also autocomplete filename.
- Added plot extrapolated fit function. Plots extrapolated fits from (0,tend) and highlights c0, y0 and tau.
- Added plot all ext/int/slice data. Plots all data + background datasets in one single plot.

- Added shortcut to copy and paste quickly any objects.
- Changed the way some data is getting backuped before saving a molecule or an embryo to increase performance and find a workaround to memory overloads.
- Fixed a bug in copy_fit where fit.fit_number was getting assigned in the wrong way. 
- Now fit object keeps track of number of iterations and function calls during fitting.
- fit object now has print_results().
- Added constrained Nelder-Mead algorithm.
- Added I_pre as a option for x0_y0.
- Added auto completion for pre folder dialog.
- Added functions get_max_int_pxs, label_pxs to create range indicator masks .
- Added range indicator to dataset_dialog.
- Added two new export functions: Export selected object to csv and export selected fits to csv.
- Added the option to also ignore frames from background datasets
- PyFDAP automatically imports useful_fcts as uf into terminal
- Changed the way average
- Added threshhold selector for better threshhold selection
- Added function that checks if objects (molecule,embryo,fits,...) are of newest version and adds latest properties to object if not yet present
- Added option for different threshholding algorithms (fixed,otsu,adaptive)
- Added option to fill values outside of embryo with nan to become better histogram and improve threshholding performance