Engine/Task/OrderedTask: Add name property

To be used by the TaskManager.
TaskManager: Show task file name of loaded/saved tasks in dialog title

Any modification of the loaded/saved state will display "Default.tsk".
Currently the name will not survive a restart of XCSoar.

In the current version saving of an (unmodified) task causes a full
Commit() to the task engine (like a modified task). This could be
optimized.

Implements trac enhancement request #1924.
TaskManager: Don't show "Default.tsk" in title for modified tasks
CrossSection: Keep shown range in sync with map zoom

Implements trac issue #2913.
MapWindow/GlueMapWindowDisplayMode: Update cruise_scale setting if auto-zoom is enabled

Needed for syncing of airspace cross-section display range.
DebugReplay: move NLineReader out of DebugReader class

Prepare creating a DebugReplay from a std::vector.
OLCTriangle: let the caller set the maximum iteration number and tree size