Add support for 'companies' property

[abarax]

Is your feature request related to a problem? Please describe.
Feature parity with the Cordova Intercom plugin.

Describe the solution you'd like
Add support to update the intercom specific 'companies' property

Describe alternatives you've considered
Can use custom attributes instead but Intercom has a special case for the 'companies' property.

Additional context
Equivalent code within the intercom cordova plugin is here: https://github.com/intercom/intercom-cordova/blob/master/intercom-plugin/src/ios/IntercomBridge.m#L185

[jpike88]

@stewones this would be a very, very useful addition

[jpike88]

https://developers.intercom.com/installing-intercom/ios/using-intercom#usage-2
scroll down a tiny bit to see iOS implementation of adding company data to a user

https://developers.intercom.com/installing-intercom/android/using-intercom#usage
scroll down a tiny bit here too