Lazy require some expensive dependencies

[hansonw]

I've noticed that language-babel often contributes ~300ms to activation time. Looking at atom --profile-startup, we can see that this is actually due to three big and easily deferrable dependencies:

It's extremely easy to get these out of the startup path by moving the require statements closer to their uses. The three major suspects in the screenshot are:

• @emmetio/expand-abbreviation (~60ms)
• fs-plus (~80ms)
• js-yaml (~150ms)

These are typically lower in practice due to Atom's v8 compile cache, but once these are lazily required language-babel consistently takes less than 100ms of activation time according to timecop.

[gandm]

@hansonw Thanks for the PR. Yes, lot of room for perf improvements!