Add a new call direction parameter to conferences for multiparty

1) Refactor ParcelableConference - too many optional params
2) Add a new call direction parameter for external multiparty
call scenarios, where a conference is assigned a direction.

Bug: 153595501
Test: atest TelecomUnitTests TeleServiceTests
Change-Id: Icb576a07b9a7a81e228babfea53474be83da7593