Improve copy/paste in tmux

Right now, copy pasting is _weird_. 

I frequently need the mouse to copy/paste as I am not just doing it [vim-style]() and with the current setup, it's not that user-friendly.

While doing a quick search, I found [this](http://stackoverflow.com/a/34908356/2020428) on SO which seems to solve it for 2.1 (and if running older, the one below it or the accepted answer seem to be good enough).
