wrapping i18n missing keys made optional

`I18n.translate` helper will wrap the missing translation keys
in a <span> tag only if `debug_missing_translation` configuration has
a truthy value. Default value is `true`. For example in `application.rb`:

    # in order to turn off missing key wrapping
    config.action_view.debug_missing_translation = false

🎉 🍻

Fix `receive` spelling

Handle specified schemas when removing a Postgres index

[ActionCable] Test invalid action on channel

Found `recieve` next to the correctly spelled method name, fixed it.

Also we prefer a one space padding within hashes, add that.

[ActionCable] test perform action with default action

This test needs to have a require for the Listen gem or else it returns
an error when run by itself or with a certain order in the Active
Support tests. We use `silence_warnings` because Listen has some
warnings about private methods. It's already silenced when it's required
in Active Support EventedFileUpdateChecker.

```
1) Error:
EventedFileUpdateCheckerTest#test_should_not_execute_the_block_if_no_paths_are_given:
NameError: uninitialized constant EventedFileUpdateCheckerTest::Listen
    test/evented_file_update_checker_test.rb:21:in `teardown'
```

The test was was in here twice so we were seeing this error:

```
activesupport/test/caching_test.rb:658:
warning: method redefined; discarding old test_local_cache_of_read_nil
activesupport/test/caching_test.rb:634:
warning: previous definition of test_local_cache_of_read_nil was here
```

Fix "instance variable not initialized" in tests

Prevent ActionController::Parameters in url_for

add line break between method of generated channel js

[ActionCable] Test available actions on Channel

Our logic is complex now and we don't need to check the version to asset
the behavior so I'm removing the checking here.

Allow normal version updates within a release series

Still more to do. Please assist!

We went back to `Thread.current[]` in 33e11e59.

[ci skip] Fix grammar

```
# before
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
  connected: ->
    # Called when the subscription is ready for use on the server

  disconnected: ->
    # Called when the subscription has been terminated by the server

  received: (data) ->
    # Called when there's incoming data on the websocket for this channel

  appear: ->
    @perform 'appear'
  away: ->
    @perform 'away'
```

```
# after
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
  connected: ->
    # Called when the subscription is ready for use on the server

  disconnected: ->
    # Called when the subscription has been terminated by the server

  received: (data) ->
    # Called when there's incoming data on the websocket for this channel

  appear: ->
    @perform 'appear'

  away: ->
    @perform 'away'
```