Merge fix-many-typos-7252: Fix many typos in Twisted.

Authors: Alex, dreid
Reviewer: habnabit
Fixes: #7252

There were many typos present in Twisted documentation (sphinx and docstrings
both) and comments; they have now been fixed.

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@43373 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb