Level limitations on shout/yell/tells

Since gold-seller spam doesn't seem like it's going away, we'll need some extra solution to the issue.

One solution would be to put a limitation based on level so that you cannot say more than 1 shout/yell every 5 minutes below level 5, or every 2 minutes below level 15 (airships being unlocked), with an end limit of 1 shout or yell per minute (20 per hour) regardless of level. While having a limitation of not being able to send more than 1 tell a minute below level 15 (airships being unlocked).

These changes would not impede new players since there are relatively few reasons why anyone would need something beyond these limits... with most of those reasons being relatively disruptive in their own right.