Refactor templates to increase template re-use and make them easier to navigate

[jhugman]

There are quite a few places where we're doing the same thing, but with minor differences in the header or footer.

e.g.

• unpacking arguments, calling method calls with and without a return value
• methods in enums, namespaces, interfaces, etc etc.
• iterating through properties to generate lift and lower methods.
• copyright & similar comments

We should investigate ways our templates could be split up and parameterized so working with templates easier for language experts and more readable.

1. Decorator stucts and rendering templates in place.
2. Using the path sub-attribute of the template attribute.
3. include directive. e.g. {% include "hotmess.txt" %}
4. Template inheritance.
5. Template importing.

This is likely a starting point / meta for smaller bugs rather than a specific piece all on its own.