Include a pin feature for tabs

[romeogiggletoes]

Hello, just recently stable released to 2.5.3 and gave us the option to make tabs more compact, but then when I told Prodigy about it, he said he uses the show only live tabs feature to make tabs less cluttered, which I had no clue existed before. I would love to use that feature, however I also want to type in some offline channels without making some temporary split. So rSherms mentioned the idea of being able to pin certain tabs so that they are always visible, which would be amazing. This would also maybe solve this issue #5027 since you would be able to pin /mentions and /whispers.