fix 'typing' to 'typing_extensions' for python3.7

[HeaIn]

ImportError: cannot import name 'Literal' from 'typing' occurs when installing SDFstudio in Python3.7.

The error occurs because tying.Literal is only available from Python3.8 and up.

It is stated that SDFstudio requires python >= 3.7 in README.md, so I fixed some codes to use Literal in older Python versions.