API updates to reflect Webex Teams rebrand

[ObjectIsAdvantag]

See #1346 for context.

The proposed changes here also introduce backward compatibility as described in the Webex rebrand documentation section:

Back in April 2018, Cisco announced a rebrand from Cisco Spark to Webex. In May 2018, starting with version TODO, Botkit reflected this rebrand by updated 'Spark' mentions from the framework API.

For backward compatibility purposes, several references are now marked as deprecated, but still supported (except for Typescript code). Please migrate your code if your find references to:

• Botkit.sparkbot() => Botkit.webexbot()
• controller.config.ciscospark_access_token => controller.config.access_token: a warning shows up in the console if your code is still using this option.

Breaking changes

• bot.type now equals 'webex' instead of 'ciscospark': there should not be any impact in your code.
• the webhook HTTP endpoint automatically created and exposed by Botkit has been changed from '/ciscospark/receive' to '/webex/receive'. Note that this change can have an impact for the Webex Cloud platform to reach your bot if the traffic to your bot is routed by a reverse proxy. To avoid any bot to break, the Botkit Webex connector will expose an HTTP endpoint with the deprecated '/ciscospark/receive' path if the 'ciscospark_access_token' configuration property is detected.

These modifications have been tested against the convos@sparkbot.io which implements various examples with the Botkit conversation object. The proposed implementation has let me take an incremental changes with no breaking changes, as detailled in the releases of the convos bot project

[jfield44]

@benbrown any objections to this one?

[benbrown]

@jfield44 No! Let me run it through the paces one more time and we can include it in the next release.

[benbrown]

Thanks for all the work, @ObjectIsAdvantag! One small note - we'll have to make these docs changes again in the botkit-docs repo once this goes live.