Split IoC chapter DocBook XML into multiple files (SPR-7467)

All <section/> elements in beans.xml >=~ 500 lines have been broken out
into separate documents with DOCTYPE 'section'. This refactoring makes
working with these files much easier in wysiwyg editors (namely
oXygen Author).

For consistency, this same refactoring should be applied to all other
chapters much larger than 1500 lines, such as aop.xml (3861), mvc.xml
(3466), jdbc.xml (3042), and so on.

beans.xml and the new section files have also been formatted for
consistency and to avoid whitespace diffs as much as possible into the
future.

Author: cbeams