Add learning feature to register players for controllers

[shawly]

It should be possible for a player to select his keyboard without manual assignment by the GM.

Verify that:

• the GM has the ability to start "Learning Mode" with a macro or a custom button
• in "Learning Mode" a popup for the GM appears which displays the current player, a button to "Skip" , a "Cancel" button and a "Back" button to navigate to the previous player (if someone else mistakenly pressed the button)
• in "Learning Mode" every time a controller key is pressed, the controller will be assigned to the player that was displayed in the popup
• in "Learning Mode" the camera should focus the character token on the map that belongs to the current player for all user sessions
• all skipped players will not have a controller assigned