[feat] Added workspace class and editor preferences at Repo, Context and Global levels with cascade

[Palanikannan1437]

• Closes #17

Summary

• Added support for IDE and workspace class configuration
• Added global level defaults (compulsorily) as soon as the user uses the Open In Gitpod command for the first time
• Added repository level defaults configuration support with the shortcut (CMD+W) (optional) -> If not configured, then global defaults are used for launching workspaces
• Added context level defaults configuration support with the shortcute (CMD+W) (optional) -> If not configured, then repository level defaults are used for launching workspaces

[Palanikannan1437]

@filiptronicek and @Siddhant-K-code, would love your review on this whenever possible!

[Palanikannan1437]

Is this ready to be merged @filiptronicek? Thank you 😄!