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

Conflicts:
	app/models/issue.rb
	app/models/user.rb
	config/locales/de.yml
	test/functional/issues_controller_test.rb
	test/unit/issue_test.rb
Include issues asigned to user's groups when using 'assigned to me' filter (#2964).

Conflicts:
	app/views/my/blocks/_issuesassignedtome.rhtml

Conflicts:
	app/views/my/blocks/_issuesassignedtome.html.erb
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

Conflicts:
	test/unit/issue_test.rb
reflect name change of tracker to type

Conflicts:
	test/unit/issue_test.rb
fixes queries watcher values
fixes wrong setting in workpackage group spec, test still fails tho
group needs to be a member to the project in order to be assignable
replace Issue with WorkPackage
renames setting
removes duplicate statements (probably merge relic)
corrects comment
adapt tests to removal of issues
removes code accidentally added by cherry-picking
whitespace fixes
removes accidentally added localization
adds changelog
Does not count number of assigned groups
assign packages to deleted user upon group deletion