upgraded hooks to 0.3.3; integrated custom changes as made for 0.2.0

Conflicts:
	middleman-core/lib/middleman-core/application.rb
use instance hooks provided by hooks instead of changing the gem’s source

Conflicts:
	middleman-core/lib/middleman-core/core_extensions/extensions.rb
as there are no more local changes in the hooks’ source, it can be unvendored and used as gem
Merge pull request #1167 from hagenburger/feature/upgrade-hooks-v3

Feature/upgrade hooks v3