Add Bookmark Handling

Summary:
Add Bookmark Handling. Adds complete bookmark support as provided by
other KDE applications like Konsole and Konqueror. This allows you to
bookmark individual folders, create bookmark folders and open them.

Test Plan:
Go -> Bookmark -> Add Bookmark
Go -> Bookmark -> [Open the bookmark you selected]

FEATURE: 171366

Reviewers: #dolphin, elvisangelaccio, ngraham

Reviewed By: #dolphin, elvisangelaccio, ngraham

Subscribers: ognarb, meven, loh.tar, cfeck, hein, kfm-devel

Tags: #dolphin

Maniphest Tasks: T5408

Differential Revision: https://phabricator.kde.org/D19926