Added support for automatically showing the Serial Monitor window. This support is controled by a checkbox menu item
in the Tools menu ("Auto Show Serial Monitor"). The feature is disabled by default and is tracked by a boolean
"serial.auto_show_monitor_window" in Preferences.txt. When "auto show" is disabled the Serial Monitor window behavior
is unchanged (i.e. if you don't enable "auto show" the IDE will work as it always has).
reviewed pull req #115. fixed a compilation error, fixed a weird behaviour of the monitor when failing to find a proper port to use, made the monitor show up only at the end of a successfull upload
removed DefaultExportAppHandler and made DefaultExportHandler handle both cases with appropriate constructor parameter