mgmt: InternalFace processes Interest asynchronously

This avoids forwarding's incoming Data pipeline to be called
within incoming Interest pipeline - this property holds for
other faces, and is expected by forwarding.

refs #1419

Change-Id: I3eb1ca84830d5d8aefe0ae67a562acdd835ca5ca
fw: NccStrategy checks existence of PitEntryInfo

Strategy cannot assume StrategyInfo always exists,
because runtime strategy change may cause a Strategy
to start handling some new PIT entry.

refs #1420

Change-Id: Ibaa4337d80c02cdf074b6390e69ce30b239796de
main: Enabling system signal handling and small reorganization

Change-Id: I568c5b57e787d44b9d6a758fd7e8cdf22222234e
Refs: 1380