removing $browser.defer(), add $defer mock, clear $defer

[vojtajina]

• get rid off $browser.defer()
• use $defer mock during testing
• $defer should have API for clearing
• scope.$apply() inside $defer callback should be optional, so that you can do low level stuff without triggering $apply
• should emit 'asyncStart', 'asyncEnd' events for scenario runner

Related issue: #469

[pkozlowski-opensource]

This was fixed in 4511d39.