Remove OS specific entries

These should be listed in a global .gitignore instead.
Merge pull request #993 from xymbol/fix-gitignore

Remove OS specific entries
Fix and augment TestCommand tests.
Ensure that NewCommand tests are run.
Fix InitCommand ignored test.
Fix ignored CLI tests.
Fix additional InitCommand test.
Merge pull request #997 from rjackson/ensure-promises-are-ran-in-command-test

Fix ignored tests.
Update CHANGELOG.md
Merge pull request #1001 from landonwilkins/patch-6

Update CHANGELOG.md
Check for ember-cli updates and display message to user if an update is available
Add ember update command and change update message to suggest running that rather than npm install

Persist checkForUpdates setting and version information via .ember-cli file
Add .ember-cli files to blueprint tests/fixture directories where needed