ticker/mock: adds debug Mock Ticker
ticker/mock: adds debug Mock Ticker

This commit adds a Mock Ticker, implementing the
Ticker interface. The ticker abides by the
behavioral requirements of the production
implementation, but also includes the ability to
force feed ticks while the Ticker is paused.

This commit also places the mock.go file behind
the debug build flag. This allows us to import
the MockTicker into our unit tests.

aakselrod/lnd,LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd