Improve exception safety with smart pointers

[elfring]

Would you like to wrap any pointers with the class template “std::unique_ptr”?

Update candidates:

• ExprEditor class
• ExprStrSpec::match()

[davvid]

Hmm, Qt object ownership is interesting.

https://doc.qt.io/qt-5/objecttrees.html

In hindsight, the ExprEditor would be better off passing this to the QTimer constructors so that we don't need to do anything in the destructor. unique_ptr wouldn't be appropriate there.

unique_ptr seems like it would be helpful for ExprStrSpec tho.