allow to export local setting into a file and import setting in another computer

[jefftham]

Is your feature request related to a problem? Please describe.
Some company may block commit to github, so user may not able to upload their setting into their gists.

Describe the solution you'd like
I suggest a new feature to allow user to export their change manually (into a file) and allow them to import the setting into vscode after.

[jefftham]

duplicate #256