Skip questions in create script if files already exist

[chrispcampbell]

The create script currently asks some questions that are unnecessary if certain files already exist. For example:

• It asks if you want to create a graph to get started, but we can skip this question if config/graphs.csv already exists.
• It asks if you want to add an input variable (or variables) to get started, but we can skip this question if config/inputs.csv already exists.
• It asks if you want to install the Emscripten SDK, but we can skip this question if emsdk is found in the directory hierarchy.

[chrispcampbell]

This issue came up in discussion item #559. I'm changing this from an "improvement" to a "bug" because the first two items on the list above can cause confusion in setting up a new project if using a template that already includes a config folder (like the "sir" example does).

[chrispcampbell]

I changed the "create" script to skip the questions that modify the graph and slider config files if there is a pre-existing config directory.

Without an existing config directory

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With existing config directory

[chrispcampbell]

I also changed the "create" script to skip the question about installing the Emscripten SDK if there is a pre-existing emsdk directory in the hierarchy.

Without an existing emsdk directory

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With existing emsdk directory