1.0.0

Main changes:

● Now FeatherNotes is a single-process, multi-window app that doesn't open the same document twice when launched. D-Bus is used for that purpose (the app's behavior is like before in non-Linux systems without D-Bus).
● The qmake compilation has been removed. Its maintenance wasn't justified with D-Bus.
● Added a warning-bar for some messages.
● Printing is done is a separate thread, so that, if it takes a long time, the app could still be used.
● Added an option for remembering the expanded state of each node.
● Added an option for saving without prompt on exiting.
● Select the text between spaces with Ctrl + double click.
● Fixed the problems in restoring of window size and position.
● Keep the search string on node switching if the search is done in all nodes.
● Fixed node renaming with transparent tree view.
● Made toolbar icons small by default.
● Enabled compilation against Qt6. The default compilation is still against Qt5.
● Removed the workaround for Enlightenment (it cluttered the code for no good reason).