tweak english, move tabs in Popup.jsx

[iamsirsammy]

This has a few small tweaks to the english localization, mostly renaming Feature Pages to history, and same for Conversation Page/Window. The localization is pretty good now, but I have two questions:

• Should I be editing the english language from src/_locales/en/main.json?
• What does the option "Always Create New Conversation Window" do? Does it save every conversation or something else

Thanks