Cleanup and move to Node v7+ (async/await)

[rayzr522]

• Updated to Node v7+ (async/await)
• Added checks in gulpfile.js for users' Node versions
• Updated every command to use async/await
• Cleaned up several bugs, inconsistencies, and oddities in commands
• Improved dynamic-imports manager to handle errors better
• Updated commands manager to handle async/await commands
• Upgraded all Node modules
• Removed a bunch of Node modules we weren't using or didn't really need
• Removed request module, we're down to 2 HTTP clients now (got and snekfetch)

[rayzr522]

I've changed the version checking in accordance with @abyssvi's wishes.