"Enable history in tabs" (enabled by default)

Disabling this would remove the forward/backward navigation on tabs. 

When disabled, left-clicking a channel would:
1. If the channel was already open, switch to it
2. If the channel was not open, open it

Note: it is possible we could have two tabs open for that channel. In that case:
1. If the channel was open (possibly redundantly), switch to one arbitrarily
2. If the channel was not open, open it

In other words, it (and this is not obvious from the description, but implied from the scenarios above) prohibits the behaviour of changing the contents of a tab. Once a tab is dedicated to a purpose, it never changes.

When disabled, hiding the disabled forward/backward glyphs (since they're non-functional in this case) is optional but probably appreciated.