Readability improvements in Logging

We now truncate Session method paths and IDs based on the Logging level
to improve Session Logging readability in logcat. If another external
session is started off of an existing external Session, the preceding
histories are replaced with "..." so that the Session information is not
overwhelming.

Bug: 26571395
Test: Unit Tests and manual tests pass
Change-Id: I9ffda3d64f1072fa6228a82a86116a5e47d18c96