#177 Coloring for brace matching

[P Cause]

If you have blank lines in a block, to help readibility, and
you are at a brace, the block gets coloroed, but it looks
strange because the blank lines have no color applied.
This can give a false impresison of which lines comprise
the block.

It would be nice to color blank lines in a block to the
length of the longest line in the block. Actually, coloring
the background of all the lines to the length of the
longest line in the block will improve the visual
identification of a block.

[Mathias Ricken]

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user_id=1075744

Blank lines should be as wide as the widest non-blank line
on top or on the bottom. Example:

------return null;
----}
#####
#####
--}

I used - to denote a normal whitespace and # to denote an
empty line that nonetheless got highlighted.

Unfortunately, with the standard Swing highlighter, this
might be a bit tricky. I also introduced a "frame" highlight
that doesn't highlight the entire text but just puts a frame
around it. Right now, it puts a frame around every line:

+-----------+
|class Foo {|
+-----------+------------------------------+
| public static void main(String[] args) {|
+--------------------+---------------------+
| System.exit(0); |
+--------------------+

Ideally, it should just be the outline of the entire block:

+-----------+
|class Foo {|
| +------------------------------+
| public static void main(String[] args) {|
| +---------------------+
| System.exit(0); |
+--------------------+

These changes could probably be done together. Start at the
class ReverseHighlighter.