Move to PyPI

[avalon60]

A new release will be forthcoming - which is mainly a rearchitecture of how the app is deployed. In short, the installation model is changing. Instead of the bespoke installer, the tool will be available via PyPI, and so it will be a case of using pip to install/update.

Upon first launch, a CTkThembuilder directory will be created in the user's home directory. This will be used to store settings and themes. A migration tool will be provided for migrating any themes from your old themes location.

There won't be full support for the new label borders in CustomTkinter 5.3, until after 5.3 hits PyPI.