If a file has been opened from the command line or via the File
menu the main window title becomes "Subsurface: filename.ext".
Title also updates if 'File->Save As' is called. "Subsurface" only
is displayed when no active file is present or post 'File->New'
or 'File->Close'.
To make this work a new public method is added - MainWindow::setTitle()
and also an enum type MainWindowTitleFormat, which should allow
more complicated formatting, such as showing the selected dives
or the total number of dives (e.g. MWTF_FILENAME_N_DIVES).
Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
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