Make template hash reflect loaded contents, not yaml file

[nhammond]

Template hash is meant to be able to compare template contents. As implemented, it is only a rough approximation of this. Since the hash is calculated on the yaml file before import, it ignores the contents of any child templates, ignores equivalent expressions (e.g. reference by filename and hash vs. reference by uuid), and considers two templates identical if their references are the same, even if the files/templates they point to have different contents. This should be calculated by the server, similar to the fingerprint used in Tasks.