Added magnifier for more precise selections (#2219)

* added a magnifierwidget

* added option to show magnifier and added option to switch to square shaped magnifier

* integrated magnifierwidget into capture

this could probably be done in a nicer way.
right now the magnifier wont show if you select via the move tool.

Co-authored-by: Silas Dohm <silas@sdohm.xyz>