Pygubu-designer

* Hot fix: Error when loading old UI files. issue alejandroautalan/pygubu-designer123

* Fix name collisions between widget ids, variables and commands. alejandroautalan/pygubu-designer115
* Fix issue with Delete key in macOS. alejandroautalan/pygubu-designer119
* Fix wiki links. alejandroautalan/pygubu-designer118

* Make more intuitive design screen labels. alejandroautalan/pygubu-designer87
* Fix options of wrap property for ScrolledText. alejandroautalan/pygubu-designer98
* Improve style of generated code. alejandroautalan/pygubu-designer84, alejandroautalan/pygubu-designer85, alejandroautalan/pygubu-designer89, alejandroautalan/pygubu-designer92
* Use black as formatter for generated code.
* Add a new context command menu to select the current item's parent. alejandroautalan/pygubu-designer97, jrezai
* Fix Toplevel preview issues. jrezai
* Fix issue when changing geometry manager. alejandroautalan/pygubu-designer77, alejandroautalan/pygubu-designer80, jrezai
* Examples updated.

* Removed Python 2.7 support, Minimum Python version required is now 3.6
* New layout editor for container widgets. Added support to configure grid with 'all' index (issue alejandroautalan/pygubu-designer76)

* Add support to use custom ttk styles defined by the user. Thanks to jrezai
* This is the last version with python 2.7 support
* Other minor bug fixes.