Refactor bookmark import using a generic Netscape parser

Refactor bookmark import using a generic Netscape parser

Relates to #607
Relates to #608
Relates to #493 (abandoned)

Additions:
- use Composer's autoload to load 3rd-party dependencies under vendor/

Modifications:
- [import] replace the current parser with a generic, stable parser
  - move code to application/NetscapeBookmarkUtils
  - improve status report after parsing
- [router] use the same endpoint for both bookmark upload and import dialog
- [template] update bookmark import options
  - allow adding tags to all imported links
  - allow selecting the visibility (privacy) of imported links
- [tests] ensure bookmarks are properly parsed and imported in the LinkDB
  - reuse reference input from the parser's test data

See:
- https://github.com/shaarli/netscape-bookmark-parser
- https://getcomposer.org/doc/01-basic-usage.md#autoloading

Signed-off-by: VirtualTam <virtualtam@flibidi.net>