spx-gui: file compression

[aofei]

~~& maybe compress file size when uploading~~

It may be better to compress file when using instead of uploading.

The file (image) size we want when using should be decided on end information such as the window size & the device resolution ratio.

Originally posted by @nighca in #410

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[TBD]

[nighca]

这个先不放到 v1.3 ，等 #411 & #412 完成后再回来看文件压缩