TSVSerialiser: Allow serialising QStrings directly
ApplicationWindow: Preserve unicode when loading/saving

Refs #9970
TSVSerialiser: add selectSection

Going into the final polish, this ought to clean up serialisation logic
a little.

Refs #9970
Preserve unicode when loading/saving

This applies to:

* Graph
* Graph3D
* Grid
* Matrix
* MatrixModel
* MultiLayer
* Note
* Table
* TableStatistics

Refs #9970