Include import of __future__ features division, absolute_imports and
print_function everywhere. Don't add unicode_literals yet for it is
harder to convert.
Goal is smoothing the transition to python 3.
Instead of recording only the most recently imported path and assuming
that all previous path have also been imported, we record all imported
paths and skip recorded paths when resuming the import.
This fixes an issue where parallelism would screw up the import order
and reimport some files. It also allows us to record singleton items.
We can apply the same strategy can be applied for incremental imports.
The goal of this class is to eliminate all checks for `task.is_album`. This is
already accomplished for the methods. Next, we want to tackle the plugin
stages.
