Improve Atom startup time (#276)

* Improve Atom startup time

Before this change, activation was done on Atom startup, whether or not you actually had any Python files open.

With this change in place, we postpone activation until the Atom Python grammar's first use.

This improves startup time of my Atom by about 100ms, fixing one of the top startup time offenders according to TimeCop.

package.json

@@ -11,6 +11,7 @@
   "engines": {
     "atom": ">=1.9.0 <2.0.0"
   },
+  "activationHooks": ["language-python:grammar-used"],
   "configSchema": {
     "executablePath": {
       "type": "string",

spec/linter-flake8-spec.js

@@ -12,14 +12,17 @@ describe('The flake8 provider for Linter', () => {
   const lint = require('../lib/main.js').provideLinter().lint;
 
   beforeEach(() => {
+    // Info about this beforeEach() implementation:
+    // https://github.com/AtomLinter/Meta/issues/15
+    const activationPromise =
+      atom.packages.activatePackage('linter-flake8');
+
     waitsForPromise(() =>
-      Promise.all([
-        atom.packages.activatePackage('linter-flake8'),
-        atom.packages.activatePackage('language-python'),
-      ]).then(() =>
-        atom.workspace.open(goodPath)
-      )
-    );
+      atom.packages.activatePackage('language-python').then(() =>
+        atom.workspace.open(goodPath)));
+
+    atom.packages.triggerDeferredActivationHooks();
+    waitsForPromise(() => activationPromise);
   });
 
   it('should be in the packages list', () =>