Rename zapp.yaml templates with `python-` prefix

This is the first step in making project templates explicit. Python-type
templates are still the default, but this begins making room for
distinction. For example, a C-based project template would be the next
logical one to build.
util: initial creation of util module

... with the class "AtomicFileCreator". This class is intended for
atomically creating groups of files/directories, and rolling back
(deleting) if a problem is encountered, such as a file already existing.
zapptemplate: initial project template code

This is meant to abstract away project file creation to allow for the
addition of more project templates.
setup.py: reformat deps list
setup.py: add `tox` to dependencies

This will be needed for python project bundling.
zappbundler: initial commit of bundling util

Currently just has python project bundling utilities, which mostly
handles fetching and bundling 3rd party pure Python dependencies.
commands: add `--template` flag to `zpm new`

This includes the default template of `python`. Functionally, nothing
changes. `python` is the default (and only template).
templates: add project_type to zapp.yaml templates