Project restructured

[machinewrapped]

Following discussions with @IlmariKu I have restructured the project, so that it is hopefully less confusing for new users.

The entry-level scripts, gpt-subtrans.py, gui-subtrans.py etc have moved into a "scripts" subfolder, along with various utility scripts. The root folder now just contains installer batch files.

When the project is first downloaded you should run the install-provider.bat file for the translation service you intend to use. This will create a virtual environment for the project and install the required modules for that provider (this helps to avoid Python's eternal compatibility problems). It will also generate a command script for the installed provider, and generic gui-subtrans and llm-subtrans.

To launch the program you should use the appropriate command script, as it ensures that the virtual environment is activated first so that the required modules are available, in a compatible version.

If you want to use multiple providers, simply run the installer for each one and choose "N" when asked if you want to perform a clean installation. The last provider installed will be set as the default, though this can easily be changed in the GUI.

If you are running in an IDE such as VS Code you should just need to add scripts/ to the path of the launch argument.

[machinewrapped]

The new structure is now implemented for macOS and (in theory) Linux. The install script has been extended to create shell scripts for each provider and the GUI, and an a for all option has been added to the provider selection.