fix mouse composable overwriting previous listeners (multi calendar)

[danielwillms]

When having multiple calendars rendered on one page, events would behave incorrectly. Due to having global variables store the listeners/emit in useMouse.js, they were dropped, when a new calendar would initialize them. E.g. Having 2 calendars, both listening to onTimeClick-Event, now clicking on calendar1 would cause calendar2's listener to fire. I stored the emit/listeners in the default function, which seems to solve the problem. Not sure if there were other reasons for having these global?