Mouse support

[X-m7]

Currently, Portfolio treats mouse clicks like touches, so single left click opens files/folders, and holding left click selects files/folders and brings up the action buttons for deleting and such. While that does work, it would be great if Portfolio can support using the mouse similarly to how other file managers do it, so then Portfolio works better on a desktop form factor as well as being great on mobile.

While one could argue that single clicking to open is the better approach (KDE used to have that as the default before Plasma 6 for example), I don't think that applies to holding down left click in order to select, copy and so on, especially since the right mouse button is currently unused. So, I think the way to improve the user experience with the mouse without having to change the existing design too much (as opposed to adding a context menu just for right clicks for example) would be to make right clicking do the same thing as holding down left click or tapping and holding.