Ability to assign issues to groups (#2964).

Option is disabled by default. It can be turned on in application settings.

Conflicts:
	app/controllers/reports_controller.rb
	app/models/issue.rb
	app/models/issue_category.rb
	app/models/mail_handler.rb
	app/models/project.rb
	app/views/issue_categories/_form.rhtml
	app/views/settings/_issues.rhtml
	config/locales/bg.yml
	config/locales/bs.yml
	config/locales/ca.yml
	config/locales/cs.yml
	config/locales/da.yml
	config/locales/de.yml
	config/locales/el.yml
	config/locales/en-GB.yml
	config/locales/en.yml
	config/locales/es.yml
	config/locales/eu.yml
	config/locales/fa.yml
	config/locales/fi.yml
	config/locales/fr.yml
	config/locales/gl.yml
	config/locales/he.yml
	config/locales/hr.yml
	config/locales/hu.yml
	config/locales/id.yml
	config/locales/it.yml
	config/locales/ja.yml
	config/locales/ko.yml
	config/locales/lt.yml
	config/locales/lv.yml
	config/locales/mk.yml
	config/locales/mn.yml
	config/locales/nl.yml
	config/locales/no.yml
	config/locales/pl.yml
	config/locales/pt-BR.yml
	config/locales/pt.yml
	config/locales/ro.yml
	config/locales/ru.yml
	config/locales/sk.yml
	config/locales/sl.yml
	config/locales/sr-YU.yml
	config/locales/sr.yml
	config/locales/sv.yml
	config/locales/th.yml
	config/locales/tr.yml
	config/locales/uk.yml
	config/locales/vi.yml
	config/locales/zh-TW.yml
	config/locales/zh.yml
	test/functional/issues_controller_test.rb
	test/unit/issue_category_test.rb
Include issues asigned to user's groups when using 'assigned to me' filter (#2964).

Conflicts:
	app/views/my/blocks/_issuesassignedtome.rhtml
renames variable invalidated by cherry-picking commit 578fdc62f26c23951b2d2c2b9be0040c7ade0634
fixes filtering by watchers broken by 9f18636
fixin' oldschool validations and broken tests

Conflicts:
	app/models/project.rb