withdraw previous notif of same kind

[teamcons]

-Fixes #114.
For each type of reminder, badger removes the older one right before notifying anew. So you never have history being cluttered by ten times the same thing.

(Darshak, my man, do we also want Badger to clean up older of its notifications upon startup? If the ones from yesterday are still here, it may be better to have badger just straight up tidy)

[teamcons]

I have a commit i havent synced up, which removes all Badger notifications upon quitting
do you want this? this way if people disable Badger then close it, or quit it, the app tidies up behind itself

[dar5hak]

Thanks, I didn't know withdrawing the notifs was this easy. 😅

And yes, we do want to withdraw old notifications upon quitting. It's mostly in-the-moment stuff and not something that needs to be preserved like, say, an email notification.

[teamcons]

Okay, ill do a separate PR, and immediately merge