Replace UserRepresenter with UserView

...roma/web/twitter_api/representers/activity_representer.ex

lib/pleroma/web/twitter_api/representers/base_representer.ex

lib/pleroma/web/twitter_api/twitter_api.ex

lib/pleroma/web/twitter_api/twitter_api_controller.ex

lib/pleroma/web/twitter_api/utils.ex

lib/pleroma/web/twitter_api/views/user_view.ex

...eb/twitter_api/representers/activity_representer_test.exs

test/web/twitter_api/twitter_api_controller_test.exs

test/web/twitter_api/twitter_api_test.exs

test/web/twitter_api/views/user_view_test.exs