Add a find by name feature to player-tracker

It search for an user name and if the user is found, center the map on it's
last known position.

The feature can be triggered by:
 - Entering the user nickname in the search box preceded by '@'
 - Ctrl+Clicking on an user name in the chat

To do that I also needed to add 2 new hooks: geoSearch and nicknameClicked.
If you consider it too big of a change for only one pull request I can create 2.

For both of them returning false will interupt the default action

'geoSearch' is called when something is entered in the search box.
The argument is the string entered in the search box

'nicknameClicked' is called when a nickname is cliked.
The argument is an object with 2 properties:
 - 'event' contain the standard event object
 - 'nickname' contain the nick of the user