Reuse weboob.capabilities.image.BaseImage to contain the image and its
thumbnail.

TODO: image data should be fetched by modules by fillobj means

This will avoid importing lxml and requests in weboob.capabilities.*

Also, add Comment in weboob.capabilites.recipe.__all__.

__str__ is reimplemented in terms of __unicode__ and __repr__ else.

In Python 2, __repr__ and __str__ shouldn't return unicode.
This caused a problem for example when logging-debug a filter on Thumbnail.url,
as the logger couldn't encode the unicode repr.

Signed-off-by: Simon Lipp <laiquo@hwold.net>

flake8 --select W391,E302,E301,E304

autopep8 can't fix W391 even though it claims it can.
Fixed using a simple custom script.