Ignore sentences where text exists in symbol

Tried to check if sentence text is equivalent to entity text. If so, do
not create respective sentence. Note: Does not work so far because
text-syntax in the affected colums is slightly different and hardly to
be generalized.
Don't repeat sentence name in sentence text
put context in block
Rev "Ignore sentences where text exists in symbol"

reported for hets, see http://trac.informatik.uni-bremen.de:8080/hets/ticket/1101

This reverts commit 38ff4b3e26780dc16fa0ef9e0fe99bb8238619dc.
began readability module for sentences
Merge branch 'master' into display_of_axioms
finished test for display of sentences, began model
Set display_text on sentences from update_or_create_from_hash.
basic link-interface #17
links
First steps to integrate Git.
Foreign key for repository_id in combination with parent_id added.
Abilities adjusted
Create (untested) git lib
Removed redundant method.
Add first tests for git lib
merge conflict
Cleaned up duplicate code.
some tests fixed
simple Links working