MTC4BT: Unify alternative direction label in config between channels and actions

[raymondbrink]

Channels now expect a value of reverse for the alternate direction. Actions require backward. Both should use the same value.

[Mattzobricks]

It might be a good idea to remain backwards compatible when implementing this change, so user configuration will not fail after the firmware upgrade.

[Mattzobricks]

To Dos:

• choose one keyword.
• support both in code.
• change documentation and example to to the chosen keyword.

[raymondbrink]

The keyword will be "backward", so a channel definition can be:

{
    "channel": "A",
    "attachedDevice": "motor",
    "direction": "backward" // "reverse" is still supported for backward compatibility
}

Event triggers based on the "dirchanged" event will remain the same as before:

{
    "source": "loco",
    "eventType": "dirchanged",
    "value": "backward"
}

[Mattzobricks]

Merged. Closing issue.