Make mouse actions visible in GUI

[allejok96]

Showing available mouse modifiers/actions in GUI would help users get the most of LMMS.

There are 3 things that makes it harder for users to discover these modifiers:

• Mouse modifiers are unintuitive, sometimes ctrl is copy, sometimes shift is copy (New default shortcuts (table) #1488).
• Mouse pointer does not give feedback when a modifier is held - only in piano roll.
• There is no info in the GUI about available mouse actions.

Hidden features are useless, and we can't expect people to read through the 8 page long wiki list of keyboard shortcuts. I came here to create a feature request for note scaling in piano roll, only to discover it has been around forever... Even tresf had the same revelation back in 2015... #1648 (comment).

I think the greatest help would come from something like a status bar (#5571). See how other programs implement this:

A line of text is simpler to implement, but Blender's way is more sleek. Combining #5261 with the Blender screenshot:

Exactly how it would present the info with shift and ctrl I don't know, but the info could change depending on where the mouse hovers, if it's pressed and if any modifiers are held.

[Spekular]

Related #5571