Write Umbraco Commerce docs for the Templating feature

[mattbrailsford]

Umbraco Commerce supports custom email, print and export templates which we could do with some docs around. We could also do with sharing the default built in templates as these are currently embedded in the RCLs. We can take a look at how Umbraco Forms distributes their themes as they are also embeded and the docs are how they share them.

Current v12 template files are attached as a means of providing access right now
UmbracoCommerceTemplates.zip