Update copyrights and licenses

This was done using the commands:

    mvn license:update-project-license
    mvn license:update-file-header
Extend copyright year range to 2013

It was done with the following shell command:

    git grep -l 'Copyright (C) [0-9]\{4\} - [0-9]\{4\}' | \
    xargs sed -i '' -e \
    's/\(Copyright (C) [0-9]\{4\} - \)[0-9]\{4\}/\12013/'

The license-maven-plugin would normally do it for us. Unfortunately, it
cannot, because we have the canUpdateCopyright flag set to false, so the
update-file-header goal cannot update the copyright year range on files
with existing headers. The flag must be false because otherwise, it
would overwrite each file's copyright holders (we have a few files with
non-default copyright holders listed, which we want to preserve).

In the future, we could address the issue by contributing an enhancement
to license-maven-plugin that splits canUpdateCopyright into two parts:
canUpdateCopyrightYears and canUpdateCopyrightAuthors.