Improve legacy client ping support.

The Vanilla/Spigot server supports all versions of the legacy client pings, but BungeeCord does only support 1.6.4 as of right now. That's why I think we should also support the older versions so users of older versions will get a working server ping and disconnect.

- For clients <= 1.6 only the second line will be removed from the motd.
- For clients <= 1.3 additionally all colors are removed from the motd because they don't support them.

**Tested and working with the following Minecraft versions:**
- 1.7/1.8 are not affected by this change
- 1.6.4
- 1.5.2
- 1.4.7
- 1.3.2
- 1.0