Bug: Themes with names that start with digits cause PHP errors

[creativecoder]

If you create a theme with a name that starts with a digit, it causes PHP errors, because the theme name is used a function prefix and PHP funciton names can't start with numbers.

We either need to

• Validate the theme name and not allow them to start with digits
• Sanitize the theme name in a way that makes sure it's a valid PHP function prefix