Make RefPatternMatcher public so that it can be used from plugins

Change-Id: Ib57ecb0796ac8203db3da19681e0bb859f7f6b50
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
SideBySide2: Don't offer to expand above the first skip bar

When a skip occurs at the start of the file only display the "down"
arrow to expand below the skip bar. Users almost always want to
see more context near the edit and are easily confused by the "up"
arrow expanding context at the top of the file, where the text is
probably just a useless copyright notice.

Same reasoning exists with the footer of the file, so hide the
"down" arrow at the bottom of the file.

Change-Id: Ia774309f7a4bc07e5313cc297d430f6dfd68d99b
SideBySide2: Remove duplicate "parent" fields in PublishedBox and DraftBox

Both PublishedBox and DraftBox had a duplicate "parent" field. Drop them
and use one field in CommentBox (super class) instead.

Change-Id: Ib2adca7ee4d631af8e9eb7f12f70a05667b2c2ce
Merge "Make RefPatternMatcher public so that it can be used from plugins"
Merge "SideBySide2: Don't offer to expand above the first skip bar"
Merge "SideBySide2: Remove duplicate "parent" fields in PublishedBox and DraftBox"