Playernames not initialized correctly

[elexis]

"Player X" instead of the actual playername is displayed in many places, for example

• in the wonder victory message ("Player X will have won in Y", see #3226)
• in the tooltip of trade carts (getTradingTooltip in utility_functions.js)
• in the tooltips for tributing resources
• in the commands.txt file (correct playernames would be needed by visual replay #9)

• If someone disconnects and another player resigns, then the name of the disconnected player will change to "Player X" in all places where the correct playername was printed before (for example in the panels or diplomacy menu). This is because updateDiplomacy() in messages.js overwrites the player data with the default playernames.

[elexis]

Solves all the issues described above, except the trade tooltip, which will be handled in #3252.