Added diff navigation
 Navigation links to move to previous edit before revision in left column or next/last edit after revision in right column.
Add working EoF and BoF checks when chunck reading.
Also isset on meta-last_change-date entry.
Add some breaks to while loops.
some refactoring
merge master in branch
Merge remote-tracking branch 'origin/master' into diff_navigation
page related changelog reading refactored to class
Update changelog unit tests
Add unit tests for getRelativerevision
update function calls to changelog functions
isCurrentPage is page dependent
Improved isCurrentRevision(), tests included
refactor PageRevisionLog into Media- and PageChangelog extending Changelog
fix not updated call, renaming
improve unittests getrelativerevision. Bit code reformatting unit tests
Improve changelog reading. Inclusive unittests for chunks smaller than changelog lines.
bugfix and reformatting changelog. small chunck unittests
read changelog with chunks of chunksize size in getRevisions()
retrieve revisions around some given revisions

With unit tests

One case is not yet fixed:
when rev1 is first rev from changelog, only $max/2 revisions are
retrieved, but it should retrieve $max revisions.
Merge remote-tracking branch 'origin/master' into diff_navigation