Add `Makefile` and `configure.php` to provide find/replace theme name functionality

### Description

In our companion template repository [create-wordpress-plugin](https://github.com/alleyinteractive/create-wordpress-plugin), we have functionality that replaces instances of `Create WordPress Plugin`, `create-wordpress-plugin`, etc. with the user-provided plugin name. The specific files that provide this functionality are `Makefile` and `configure.php`.

We should implement this feature in `create-wordpress-theme`

### Use Case

1. Use `create-wordpress-theme` to create a new theme
2. Notice that there are multiple instances of `Create WordPress Theme`, `create-wordpress-theme`, etc. which need to be manually updated with the theme name.