Update to newer sentence-transformers with offline usage and renaming of classes to match the released package

[racinmat]

This PR fixes several things and it's both #113 and my own additions and fixes.

• PR Modifed masking before pooling - Fixes issue in ONNX conversion #92 renamed few classes, introducing incompatibility with the previous released versions. This should not be happening between patch versions, thus this PR reverts it.
• increasing patch version in setup.py
• now, the instructor can be used in completely offline settings with model stored locally, without touching internet, with newer sentence-transformers
• increased minimal version of sentence-transformers to reflect the change
• uses device instead of _target_device, this does not change the behavior, but get rids of annoying deprecation warning.

@hongjin-su please, review and merge this PR if you find it ok, thanks.

[mijalapenos]

Thank you for the PR, seems to work with the latest sentence-transformers for me! I hope it gets merged soon.

[racinmat]

Glad to hear it from fellow CTU student.
I hope it will get merged too, we are currently using my fork in production and it works well.
Tagging other maintainers: @taoyds @Harry-hash