feat(cache): localstorage cache js and css files

[EYHN]

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What kind of change does this PR introduce? (check one with "x")

• Bug fix
• Feature
• Code style update (formatting, local variables)
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Description

demo: https://eyhn.github.io/hexo-test/
说不定会出现问题，请验证。

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[EYHN]

ok 我检查了一边 觉得没什么问题了

[neoFelhz]

This chang was very important and experimental. I think we need to run a test on browserstack.
@cubesky @viosey

[cubesky]

Yes, We should test for this carefully.

[iblh]

+1