Patch Center

[qwedc001]

本 issue 是一个 patch 中心的追踪 issue。
This issue is a tracker to developing the patch center feature for HydroOJ.

• server side by undefined-moe
• client side (through a11y plugin) by qwedc001 (inviting FrexCheat)

TODO:Auto fetch corrisponding version's patches from hydro.ac and apply to OJ during startup and after finishing daily tasks(restart required).

client side also needs a cache control system.