Build: use browserSets from config file; allow to override
Build: set default testswarm timeout to 15 minutes

We're not testing on IE6-7 anymore.
Tests: Simplify "testTimeout" option
Tests: Remove uselss "keys" helper
Tests: Remove QUnit start hook
Tests: Simplify globals cleanup
Tests: Remove Sizzle intergration tests

Fixes #14818
Tests: More improvments for testrunner

Conform to style guide and simplify it
Build: Use jscs to check test helpers

Also fix issues found by jscs
Build: Add lint task
Tests: Correct logic of a broken assertion
Tests: Improve jsonp tests

Since global variable for callback always would be equal to undefined value
it better to check for boolean instead
Tests: Do global clean up in teardown function
Tests: Move some of the Sizzle tests to selector
Tests: Copy Sizzle.contains tests
Tests: Copy Sizzle.uniqueSort tests
Tests: Add test for selectors with commas
Tests: Add more tests for Sizzle attributes
Tests: Copy some Sizzle combinators tests
Tests: Remove unused variables