[Dialogs] Fix for #1618

- Fix for #1618  
- Remove hardcoded window sizes.
- Add new method to return dynamic homogeneous size for secondary dialog windows and modals.
- Allow resize of secondary dialog windows.
- PEP8 / Lint compliant.
- Add missing DocStrings.
- Short Fix but allows future improvement of get_modal_size helper function and avoids hardcoded integers.

Brancho: fix/remove_hardcoded_window_size  :tangerine: