Added timing signal text filtering to QT Gui

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Allow filtering signals by text This filter also applies to the plot all / none buttons Not that QT familiar so happy for advice on different approaches to this

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(pending further update)

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Gave this one another go

• case insensitive text filter
• extra buttons for adding / removing only the filtered entries to the plot
• made the columns sortable (by clicking the headers)
• That way you can easily filter then click to sort by the slowest functions (for example)
• The default sorting on launch is ascending name