[REFACTOR] renamed send* methods in ITransmitter interface

The send methods are generic and have nothing to do with Saros session
users.

Change-Id: I3e382d9a49bb13c041ddfae1014eb014fe28e71e
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1603
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>