Fix Frontend Bugs

[jamesgeer]

Closes #44. Closes #65.

Summary:

• "Add Account" no longer automatically logs user in if they have logged into Twitter before on their browser.
• "Add Account" button now allows for a window to be opened with each click, before it required a page reload.
• Login window now opens a quarter of the way down the page instead of the bottom.
• Switching account from the drop-down menu now automatically shows the new user's tweets/papers.
• "Sign in" button now says "Logout" when logged in but not selected an account.
• Logout now clears all caches.