e5e9be4

[GocTruyenTranhVui] the sign in row must not stay disabled

The app greys its "sign in" row out as soon as isAuthorized() returns true,
so the token has to be handled carefully:

* the token was cached for the whole session, including the "there is no
  token" answer, so an account added in the WebView later was never noticed;
  it is now re-read on every isAuthorized() call and only remembered between
  requests;
* "Bearer <jwt>" handed out by the site is now checked for its "exp" claim —
  an expired token keeps the row enabled, so the user can sign in again
  instead of being stuck with an unusable session;
* getDetails() now retries the chapter request once with a freshly read token
  (same as getPages already did), so a sign in performed after the failure
  takes effect without reopening the manga;
* cancellation is no longer swallowed by the request helpers.