Cleaning Up

1. Adding more descriptive comments
2. Modified name of "return_values_dict" to dict_return_values
	- This way, it conforms to Hungarian notation used in rest of the file.
3. Shrank scope of try-except block
	- Moved code resetting the theme and saving the new theme to the return values dict
	outside try-except
	- try-except now sets "string_next_theme_name" and dict saves this before being returned.
	"string_next_theme_name" is either DEFAULT_THEME (if error) OR the next valid theme in THEMES_LIST.