Add option to pin multiple notification columns with different notification types

[jmcken1]

One great feature in TweetDeck is the ability create multiple columns of the same basic type, and then customize filters for each column so they show different specific things. For instance, I create two “Notifications” columns for each account, with one set to show only mentions & quote-tweets, whilst the other shows everything else (likes, retweets, etc.). It would be handy if we could do something similar in Sengi: create two (or more) Notifications columns, and pick-and-choose which columns show which types of notifications.