[B] Improve consistency for usage message in effect command. Fixes BUKKIT-5375

**The Issue:**
When the usage message is sent to the player, It only sends the message, without specifying "Usage: "

**Justification for this PR:**
This PR helps with command usage & helps to provide consistency between commands.

*Consistency Proof: https://github.com/Bukkit/Bukkit/search?q=sender.sendMessage%28ChatColor.RED+%2B+%22Usage%3A+%22+%2B+usageMessage%29%3B&ref=cmdform*

**JIRA Ticket:**
https://bukkit.atlassian.net/browse/BUKKIT-5375

**Testing Material**
Compiled changes from local fork and tested.

Associated Bukkit PR: https://github.com/Bukkit/Bukkit/pull/1027