Bookmarks

[francesco-gaglione]

Pr linked with #353

Working on this while waiting for the design discussion

[francesco-gaglione]

The implementation in this pull request is a working implementation. I know that this functionality needs to be revised by the graphics team. In the meantime, I have implemented this functionality by modifying the UI/UX as little as possible.
Initially I wanted to put icons in the list view as in the gnome file, but this was not possible due to a bug in the row button. So I moved the addition/removal of the bookmark to the context menu (this way the UI is not changed).
The current implementation will probably not be the final one, it can be extended further (especially in terms of the UI) but it is already working and may be useful for alpha 2.