SpiffyTitles: global cooldown

[butterscotchstallion]

While there is a cacheLifetimeInSeconds setting now, it would be useful to have a global cooldown for sending link titles to prevent the bot from flooding. Consider Abusive User:

• Abusive User spams his blog 5 times in a row
• Bot caches link after the first time
• Bot is now flooding the channel with titles. Although being served from cache, the bot is still flooding