修复由于 PHPSESSID 启用了 httpOnly 导致的后台不可用

[boomzero]

What does this PR aim to accomplish?:

本版本修复了由于 PHPSESSID 启用了 httpOnly 导致的后台不可用
This fixes #847.

How does this PR accomplish the above?:

Use GM.cookie.set to overwrite the httpOnly cookie with a one that we can access.

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