security: Fixing compilation errors and providing backward compatible interface for Signature*

This commit includes missed includes and "re-introduction" of
setKeyLocator method into Signature interface.  This method was used in
dependent applications as part of SignatureSha256With(Rsa|Ecdsa) data
structures.

Change-Id: I788f687600bb2729ea8265e23d4a31b990b8ed96
Refs: #1750, #1755
security: Introduce unsetKeyLocator method into SignatureInfo and Signature

Some specific signature types also provide an advisory (non-virtual)
override for unsetKeyLocator that disables reset and throws an
Exception.  As before, if an application really wants, it still can
unset the KeyLocator by setting a new SignatureInfo without the
KeyLocator.

Change-Id: Ibefd5f9ffbcb91f8a83e76db8704cba1b984f914
Refs: #1750
face: Fixing a small bug with Face::shutdown

Face::shutdown did not properly shutdown the Face (io_service) when
"always block" mode was used (Face::processEvents(..., true);)

Change-Id: I6bedcf2b45be1506e6b4a94759d1b5168e107252
face: Issuing Transport::connect() within the same thread as Transport::send()

In certain cases, previous version caused connect() to fail (stopped
io_service due to exception) before send() is dispatched.  This could
have resulted in incorrectly calling Transport::send with old buffer
when io_service resumes.

Change-Id: Ib6ba0f1d87ec321da0c489eb41850b5b401e5521
Refs: #1759
interest: Allow in-wire refreshing of Interest's nonce

Change-Id: I47500fce16a1d37af865d3f9dab59355d6108c95
Refs: #1758
transport: Cleaning up transport when failure occurs

Change-Id: I9b4f6f223637dc1f683c628f21171ebc3b9563da
util: Introduce Scheduler::cancelAllEvents to cancel all previously scheduled events

Change-Id: I11e736bec855fe4122915486faec369237cf64a6
Refs: #1757