added first draft of documentation on how to label a corpus

we're missing documentation on the home page because is not done yet
also we don't tell anything about creating an user and login in.
changes on how to run it
Merge branch '313-labeling-tutorial' into develop
Swapped fact extractor for relation extraction classifier
Erased obsolete features
Updated tests to the new classifier
Updated default classifier config
Merge branch 'replace-factextractor-for-relation-extraction-classifier' into develop
Added threshold calculation to achieve high precision / high recall
Removed old fact extractor experiment runner and replaced it with relation extraction classifier experiment runner
Merge branch 'hiprec-hirec-knob' into develop
stopping pre-process if the stanford corenlp fails
Merge branch '340-corenlp-bug' into develop
added first draft of documentation about how to start with iepy
separated instantiation to it's own doc page, and core's doc into their own page
removed old landing page in order to wait for the new one
Merge branch '316-usage-documentation' into develop
Updated tests to new api
Updated old files to new api
Merge branch 'bugfixing' into develop