Add activationHooks

[aviatesk]

Hi, this PR suggests ide-css uses activationHooks for better loading time.

Purpose

Introduce actiavationHooks:

• Only activates this package when an user actually uses
  • It gets activated when an user opens files with CSS/LESS/SCSS scope (or s/he switches to one of them from the other syntax scope)
• Better package loading time in a case that an user doesn't open CSS/LESS/SCSS files throughout the Atom process

Notes

The difference from enhancedScopes:

• enhancedScopes only controls the scopes where this package can be used AFAIU

Fallbacks

I've never noticed the downside of this change

Misc

You can see ide-typescript, the officially maintained Atom-IDE package, uses this logic as well: https://github.com/atom/ide-typescript/blob/master/package.json#L68-L73

[aviatesk]

@liuderchi Anymore update on this ? Or are you just against this change ?

[liuderchi]

@aviatesk Sorry for the late response. Let's merge it!

[aviatesk]

Thanks so much for merging !

I would appreciate if you would make an new release, so that I can use it on different machine easily ;)

[liuderchi]

@aviatesk v0.3.3 has just released 🙂