Do not emit activated signal when keyboard modifiers are on.

Allow to use Control/Shift/Alt/Meta to select/deselect files without
opening them.
Activate view items only if clicked with left mouse button
Fix crash when context menu is requested but selection is empty
Fix middle click position calculation in detailed view mode
Close tabs by middle click
Makes the "Show Hidden" option be saved in settings file and properly loaded. I don't understand why it was not done yet, bu here it is.

I'm not sure if I called settings.save() in the right location, but here
it is, and fixes #56.
Make settings of size of icons be properly loaded

This fixes SmallIconSize, SidePaneIconSize and ThumbnailIconSize.

Fixes #44.
fixed selection issue #45
Adds history menu on right-click on history arrows
Merge remote-tracking branch 'upstream/master'