Fix value label mouse/keyboard interaction

Summary:
After commit e5cc92b8 ("Make text from Dolphin's information panel
copyable") links were no longer activatable, and the full URL is not
retrievable in case the target was partially ellided. Set
TextBrowserInteraction for links. This implicitly creates a "Copy Link
Location" entry in the Context Menu.

Also remove the TextSelectableByKeyboard flag - this implicitly creates
a cursor "|" symbol whenever one of the labels is clicked, and the cursor
can not be removed again (only by selecting a different file). The text is
still selectable using the mouse.

Depends on D25240

Reviewers: #baloo, ngraham, astippich

Reviewed By: #baloo, ngraham

Tags: #baloo

Differential Revision: https://phabricator.kde.org/D25241