Fix work directory cleanup : never go deeper than one subdirectory

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Merge branch 'testing' of github.com:jflesch/paperwork into testing
Merge branch 'testing' into unstable

Conflicts:
	src/paperwork/backend/docsearch.py

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Add label sklearn estimator
	dependencies : sklearn, scipy, numpy, skimage
	The documents with labels are used to train a collection of
	supervised classifiers.
	Each label got a classifier (OneVsAll strategy)
	The prediction are made at index time : non labelled documents
	are filled with an estimated predict_label_list
	The whoosh search takes into account the predict_label_list
	Older documents may not be correctly predicted according to the
	new document (online learning), so it can be usefull to reindex all
	TODO: we might want to save the thumbnail in a cache file for each doc
Add prediction to doc member and gui (bold unchecked labels)
PEP 8 corrections
Change THUMB_WITH constant in BasicPage
Small corrections according to code review
Remove static for _update_doc_in_index
Tune fit_label_estimator so it doesn't refit all estimators when not needed
Add code comment
change typo
Change constant name
Change callee for more significant meaning
Optimization of reload_index