Add tooltip or notification about training increment with ctrl

[GreatApo]

Somehow inform the users that by pressing CTRL the training increment buttons change by 10 instead of 1. (#450)

[jrel]

CTRL doesn't work on Mac. We can use e.metaKey to check if the command key is pressed, but meta is the window key in Windows.
We can add a filter to check if the user uses a Mac.

var isMac = navigator.platform.toUpperCase().indexOf('MAC')>=0;

But I think it is easier to switch to the shift key and use e.shiftKey.