Bookmark Manager:
Delete folders, rename them, create new ones, delete bookmarks and edit bookmarks (including moving to other folders).
Also adds support for importing .kml files.

The only missing thing -- which I plan to make a junior job -- is drag & drop support.
(Internal move to change the order of folders and bookmarks inside folders. Maybe also D&D between views to support dragging bookmarks quickly to other folders.)

Squashed patch of a local git branch:
- Support importing bookmarks from .kml files. When conflicts arise (imported bookmark already exists), the user is asked whether to skip the new or replace the existing bookmark.
- NewFolderInfoDialog is a misleading name. Rename it NewBookmarkFolderDialog.
- Rename NameDialog to NewBookmarkFolderDialog, the former is too generic. Fix broken license header in NewBookmarkFolderDialog.h. Make it possible to use the dialog without changing existing bookmarks directly. Use a ButtonBox in the .ui to get a consistent interface.
- New bookmark folders can be created within the bookmark manager.
- Deletion of individual folders and bookmarks. Use the first folder as default selection.
- Use the existing dialogs to edit bookmark folders and bookmarks in the bookmark manager.
- Rename BookmarkInfoDialog to EditBookmarkDialog which describes its purpose better.

REVIEW: 6411