Test framework v2

[freakboy3742]

A revised approach at template modifications to support testing in a iOS Xcode project.

Includes the gross project layout changes from #12, using the class name rather than the app name as the project directory; this is the bulk of the changes.

The significant changes are:

1. Modification of app startup to use metadata to choose the name of the app module.
2. The disabling of optimisation in the runtime interpreter
3. The addition of a metadata entry in briefcase.toml pointing at the Info.plist file.4.
4. Removal of the use of Py_DecodeLocale (which is recommended by the Python docs).

Refs beeware/briefcase#962

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct