Make SlashCommand#getHelp() return translated text when available.

[Andre601]

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Description

This overrides the getHelp() method to return a translated description using the default locale through getDescriptionLocalization().get(TranslateUtil.getDefaultLocale)
This should allow a user to set the description within the localization files without needing to set the help text itself.
Should there be no localized description for the default locale (Be null or empty) will it default to using this.help

This also adds getDefaultLocale() in the TranslateUtil to retrieve the default locale that was set.

I didn't add the same functionality to the name, as names in SlashCommands need to be alphanummeric when creating, which with this aproach would be problematic.

Given that this overrides a method for SlashCommand, should it automatically also be applied to Subcommands too.

Closes #89

[Chew]

After testing this I think the solution here might be setting this.help to "null" by default then falling back to "no help available" if there's no help in that locale. However, Discord natively uses fallback to whatever language is available, so it's really not a big deal here. Frankly it should be deprecated entirely, but that's not the scope here.