0.5.0

Main changes:

● A shortcut editor is added to Preferences.
● The Preferences dialog size is always remembered.
● Smarter Shift+Enter, especially with numbered lists.
● Auto-replace some strings while typing.
● The selected text and highlight colors will be set automatically if those of the app style aren't suitable.
● Better placement of text context menu actions.
● The current item is kept during a tree DND.
● Tree nodes are dragged only if there is a real mouse movement (and not when the view is scrolled by the wheel of a motionless mouse).
● On triple clicking, select the current block without selecting its newline or start/end whitespaces.
● Smooth scrolling with mouse wheel.
● The Qt methods that were deprecated by Qt 5.13 are replaced.