reuse last used color for newer text boxes (only if applied globally) + recolor text boxes on background changes (white text becomes black and black text becomes white (like for polygons))

This reverts commit 08f7b3c1.

fixed a bug where clicking on/moving a textbox by its rubberband whith stylus tool on text caused a crash (more frequent after zoom out)

Revert "workaround to adress badly attached thumbnail views (no more time to investigate on it...) + prevent overwriting scenes"

This reverts commit 0fd15f62.

workaround to adress badly attached thumbnail views (no more time to investigate on it...) + prevent overwriting scenes

This reverts commit b6f41165.

Previously, items such as audio, video, and widget items could not be
cut and pasted because when the page was saved, any item that had been
deleted was permanently removed (including its source file, in the case
of these mulitmedia items).

This commit prevents the deletion any item in the undoStack
(i.e, items that have been deleted) when the document is persisted,
meaning the source file is still available when pasting the item on
another page (or document).

Note that this can lead to cases where the source file is kept in the
document even when no item is present. This should be a relatively rare
occurence, however.

This fixes two related issues:
1) When taking a partial screenshot of the desktop, then copying it
(Ctrl-C) and pasting it in a new document, it was not saved
2) When a page of one document was copied into another (in document
mode, by dragging the page onto another document), media files
disappeared from the new page.

Bug likely surfaced when fixing positioning of saved strokes. Quick
tests show that positioning now works both for duplication and
saving/loading

This was observed in some cases on low-resolution screens, at least on
Linux and Windows.

The previously hardcoded value for the width of the text items' titlebar
(consisting of the buttons for formatting text) was replaced by a
method calculating its width (which varies based on screen resolution).