Option to ask User Gist Description Before Creating new Gist.

[shanalikhan]

When user creates new Gist to upload

Extension need to ask user the Description of Gist - such as :

1. Office Vscode Settings
2. Home VSCode Settings

This feature should be enabled by default. But if anyone dont want to be keep Description can be disabled from the code settings by name sync.askGistName in the code settings.
It will always keep the Default Gist Description defined in localSyncSettings file.

This feature provides a path to implement #308
Allowing user to set name of Gist before creating, so #308 will show those names when downloading the settings.