Menu Page Notice/Error Classes

[jaswrks]

Related to https://github.com/websharks/s2member/issues/1034. Recent versions of WordPress use CSS classes notice notice-info, notice notice-error instead of updated and error, which are what Comet Cache uses. While updated and error are still valid, it would be better if Comet Cache were improved in this respect. All notices should have the .notice class, and then be given the appropriate additional class based on the type of notice it is:

• notice-info
• notice-success
• notice-warning
• notice-error