Easier Child Theme Development

Surrounded function definitions with code that checks to see if the function is already defined. This change allows for easier child theme development. It is a [recommended practice](https://codex.wordpress.org/Child_Themes#Using_functions.php) for theme developers.

Note: this change was done use regular expressions; only basic testing was done to ensure problems didn't exist. I tested these changes using [my child theme](https://github.com/nathanph/fruitful-child).

Expressions:
Find: ^function (?'functionName'[^[\s(]*]*)(?'functionCode'.*?)^\}
Replace: \nif\( !function_exists\('$+{functionName}'\) \) \{\nfunction $+{functionName} $+{functionCode}\}\}