Allow selection of start-script template for server pack config

Allow users to select templates on a server pack config basis, meaning:

Global config:

• default Powershell-script template for all new configs
• default Shell-script template for all new configs

Server pack config:

• Filepicker for shell-script template(s)

The global config is what every new server pack configuration receives. The pack specific option overrides the global one and can be used for further customization. Example:

1. New config gets Powershell and Shell templates
2. User changes template selection to only Shell template
3. Server pack now only generates a Shell script