Remove two copies of underscore.js from Meteor, using NPM package instead.

Follow-up to 27382c6. A step towards addressing issue #302.

We still have one copy in the underscore smart package, for serving to clients.
Fix increment-version script for bundled underscore
Increment version to 0.5.3.
Start on History.md for 0.5.3.
Spark: Test that patching "<input type=checkbox/radio checked>" onto unchecked
input works.

This test was extracted from a fix for this specific issue #478 which
accidentally never got merged; 442b86eebd ended up fixing this issue with a
slightly different change than the unmerged fix.
Finish first draft of 0.5.3 release notes.
Remove some no-longer-true caveats about Minimongo from docs.
Adding expiresAt property to Google login data for accounts-google. fixes #525
Some minor modifications to 79405a495d4acaffc56042f8f7e15b5b34b6171f
Removed linkedin package from this PR

Login services should be defined from within their packages

Corresponding login service assets (images and css should be in their respective packages not inside of accounts-ui-unstyled)

Conflicts:
	packages/accounts-linkedin/linkedin_client.js
	packages/accounts-linkedin/package.js
	packages/accounts-ui-unstyled/login_buttons.js
	packages/accounts-ui-unstyled/login_buttons_images.css
Tests for the functionality we want
Accounts._loginButtons.getLoginServices returns unique services

This may be improved by passing an iterator to _.uniq instead of doing
this malarkey I did for the first run with JSON stringify and parse. ^_^
Add password to the available service buttons if it's included
Vastly simplify by removing the JSON parsing.

Instead, just run _.uniq on the Accounts._loginButtons.loginServices.
DUH. PRESTO!
Variable declarations on one line; self instead of that.
Remove uniqueness check. Devs shouldn't be idiots :)
Make sure password is last
Oops, we should memoize the last service in case we need to swap
Remove whitespace
Simplify and fix accounts-ui listing of login services