Set the window title to the currently loaded log file name

[stmoon]

When I use multiple PlotJuggler applications, I am always confused about which PlotJuggler window is associated with the log I am looking for.

To alleviate discomfort, I set the window title to the loaded log file name. It's a simple function, but I believe it's incredibly helpful.

[zdavkeos]

@stmoon I pulled your branch and built it, and I do like your change. However, I think it needs to be taken a little further:

• There is already a feature to set the window title at startup (see mainwindow.cpp), this should not be overwritten.
• The title doesn't change when you start streaming; this would be a very nice addition.

Let me know what you think.

[facontidavide]

This will not work when loading multiple files

[Jofkos]

This will not work when loading multiple files

Having the title be "{first filename} and others" would still be helpful.