Move the logout button to the settings menu.

Notes:
- I'm keeping the login button on the menu sheet.
- Hitting the resituated logout button still takes you to the login form.
- I failed to find the source of logout css class special behavior, so
  didn't change the now misnamed "logout" class on the menu sheet to
  login.  That should be rectified.
- I included the settings-residing logout button in the section with the
  account name, in contrast to where it is in the native iOS version.
Merge pull request #342 from SpiderOak/issue-338-move-logout-button

Move the logout button to the settings menu.