Adding support to actually set breakpoints on the debuger side

Adding support to actually set breakpoints on the debuger side

* Source/Breakpoint.h: New debuggerId ivar to keep track of the engine's tracking ID
* Source/Breakpoint.m: Synthesize ivar
* Source/DebuggerConnection.m/h:
([DebuggerConnection addBreakpoint:]): New method
([DebuggerConnection removeBreakpoint:]): New method
* Source/DebuggerWindowController.m:
([DebuggerWindowController gutterClickedAtLine:forFile:]): When adding a breakpoint, tell the engine to set it