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

[nikkifurls]

Description

In our companion template repository 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.