Creating a project with kabob-case causes errors

When using `mix phoenix.new some-kabob-case`, you'll get this error:

```
** (Mix) Application name must start with a letter and have only lowercase letters, numbers and underscore, got: "some-kabob-case". The application name is inferred from the path, if you'd like to explicitly name the application then use the `--app APP` option.
```

With Firebird, it creates the project anyway, which then screws up the project.


We should implement the same protections as Phoenix's generator (or push this upstream if it's an upstream problem).

Start by reproducing the `mix phoenix.new some-kabob-case` command and compare its behavior with Phoenix's generator protections. Identify the Firebird generator entry point from that command, then confirm that invalid project names are rejected before a broken project is created.

Written by the indexing model from the issue text.