CMS-1834 Add type definitions for account_delete in RemoteService.ts

Add strict typing for the parameter and result values of RemoteServiceInterface.account_delete()

* Check the RpcHandler method in Java to find the exact values accepted and returned.
* Use optional types (optParam?: string) where appropriate.
* Avoid use of any as much as possible and use concrete types.
Merge branch 'master' of github.com:enonic/wem-ce into CMS-1834

Conflicts:
	modules/wem-webapp/src/main/webapp/admin2/api/js/lib/RemoteService.ts
Merge pull request #277 from enonic/CMS-1834

CMS-1834 Add type definitions for account_delete in RemoteService.ts