ImportAdded support for in-place and link imports

Fix for the `ImportAdded` plugin crashing during in-place imports (#1107).

Add support for the new link imports introduced in Beets 1.3.9.

Note that link-imports that preserve file modification times will follow
the links and preserve the mtimes on the link targets. The mtimes on the
links aren't modified.
ftintitle: Remove empty ui.print_() call.
ftintitle: Use log.log() instead of ui.print_().

Fixes #1172.
Add a missing space
Merge pull request #1170 from silb/importadded-in-place-link-support

ImportAdded support for in-place and link imports
Changelog for #1170
Fix handling of duplicate album artists in ftintitle

The code that determines the featured artist part of the artist only
handles two element lists. When the album artist is duplicated, it
splits into a three element list causing no featured artist to be found.

This ensures the albumartist_split can ever only have 2 elements.

Fixes #1179
Merge pull request #1176 from Freso/issue-1172-ftintitle-less-import-verbosity

ftintitle: use log.log() for outputting
Changelog for #1176
Merge pull request #1181 from marcaddeo/fix-ftintitle-duplicate-album-artist

Fix handling of duplicate album artists in ftintitle
Changelog for #1181
changelog: #1175 is unrelated to the fix in #1176
Merge pull request #1182 from Freso/patch-1

changelog: #1175 is unrelated to the fix in #1176
Catch exception when program check has non-zero return code

See #1175.