specification: Rename additions/jar to external

For use by the C++ code where this name is inappropriate in the
install tree.
specification: Add XML catalogues for all released XML schemas
Merge remote-tracking branch 'origin/develop' into specification-catalogue2
cpp: ome-xml: Install external schemas and catalogue files
Ordered MapPairs implementation

After feedback from the client developers, the contents
of the MapPairs class which was previously a string-string
map has been converted into a list of string-string pairs.

The `getMap()` method is now `getPairs()` and where possible
mutation of the contents is prevented, e.g. by making the
fields of MapPair immutable and using copy-constructors
rather than setters where possible.

Still slightly unclear is if the naming of the "map" is
correct now that it's no longer based on a hash map, and
whether the value of the MapPair will ever need to be anything
other than a string.
Add guava to the bundle jars
Fix base64 decoding

This limits the number of bytes read, so that the entire stream is not
decoded for every plane.  It also removes the extra encoding step in
favor of trimming the already-encoded base64 string at the first "<".
Fix copyright statement
Set the encoding to ASCII to handle units.

The sample files should now work.
Merge pull request #20 from jburel/ome-xml-fix

Set the encoding to ASCII to handle units.
OME-XML: prevent IndexOutOfBoundsException if BinData is empty
Merge branch 'ome-xml-fix' of github.com:melissalinkert/bioformats into ome-xml-fix
PNG: reduce the amount of memory needed to read most tiles

The very last row of tiles will still require the full image to be
read, however.
cpp: xerces: Throw exception on EntityResolver failure
cpp: test: Update xerces schema paths
Merge remote-tracking branch 'origin/develop' into specification-catalogue
Merge branch 'cpp-xercesfix' into specification-catalogue
Handle empty binData tag.
Merge pull request #21 from jburel/ome-xml-fix

Handle empty binData tag.
PNG: use a custom InputStream implementation for decompressing images

This prevents us from having to read the entire compressed stream into
memory before decompressing.  See #12274.