Raise Error::CookieError more often

[152334H]

Related to #55 #57 (not #60, that is unaddressed in this PR)

Previously:

$ leetcode t 1 [INFO leetcode_cli::plugins::leetcode] Sending code to judge... error: expected value at line 1 column 1

Now:

$ cargo run t 1 Finished dev [unoptimized + debuginfo] target(s) in 0.06s Running `target/debug/leetcode t 1` [INFO leetcode_cli::plugins::leetcode] Sending code to judge... error: Your leetcode cookies seems expired, please make sure you have logined in leetcode.com with chrome. Either you can handwrite your `LEETCODE_SESSION` and `csrf` into `leetcode.toml`, more info please checkout this: https://github.com/clearloop/leetcode-cli/blob/master/README.md#cookies

I have introduced a general method, is_session_bad(), which should reliably answer the question of, "is LEETCODE_SESSION invalid?". Emphasis on should, because I have attached no additional tests in this PR as well.
Some of the code added is not very good. Please edit/criqitue as you see fit.

[clearloop]

Great! thanks!