Add postgres folder type

[Kleywalker]

Fixes #IssueNumber

Changes proposed:

• Add

Add postgres folder type

[Kleywalker]

Based on the official logo: https://en.wikipedia.org/wiki/PostgreSQL#/media/File:Postgresql_elephant.svg

[Kleywalker]

Inspired by the mysql folder type icon: https://github.com/vscode-icons/vscode-icons/blob/master/icons/folder_type_mysql.svg

[robertohuertasm]

Thanks for your contribution. I tried to push to your branch to rebase and remove the conflicts but couldn't do it. So please, rebase whenever you can. Also, please, keep the alphabetical order of the folder declaration.

Finally, about the non light icons, I'm wondering if it wouldn't work for all themes just the blue one, by keeping the black line around the elephant.