Implement templating system

[bsutton]

I'm interested in creating a template system. When you create a project you can start with an existing library of your own or we will generate one for you. It might be useful to have a small library of starter templates that demonstrate common techniques when using dshell.

dshell create from <template>

Templates would live in ~/.dshell/templates

Then give the user the ability to list, add and delete templates of their own.

We should have two subdirectories under templates:

• builtin
• user
  This will allow us to upgrade the builtin templates without risk of interfering with the user templates.

Should we allow a user to create a template with the same name as a builtin template?

We should could allow a user to create a template with the same name as a built in template as a way to 'override' the standard templates.

If this is the case then we should warn the user before creating the user template.

[bsutton]

For Pub-install/run native CLI applications, you can put files in the package's lib/ directory and use Isolate.resolvePackageUri to find them. This works because the "deployment" of pub packages to the pub cache retains the entire lib/ directory.

[bsutton]

Builtin templates should be located in the lib/templates folder.

The dshell install #12 command will copy the builtin templates from the packages lib/templates folder to ~/.dshell/templates/builtin