Add copyright headers *before* package statement
Remove erroneous license-maven-plugin includes tag

This tag was preventing the plugin from properly processing any files.
Add missing eof newline
Update more copyright year ranges

This was done using:

    mvn -P all license:update-file-header

They were missed the first time due to a misconfiguration of
license-maven-plugin, which has now been corrected in
ca7def255cd2681d89071ab4b4112adabd5347c5.
Update even more copyright year ranges

These were done manually (found using "git grep 'opyright.*2012'"),
since license-maven-plugin did not catch them.
AboutImageJ: use copyright range to current year

Elsewhere in the project (i.e., in copyright headers and LICENSE.txt
files), we use a date range rather than explicitly listing every year.
According to the GNU GPL How-To guide:

    For software with several releases over multiple years, it's okay to
    use a range ("2008-2010") instead of listing individual years
    ("2008, 2009, 2010") if and only if every year in the range,
    inclusive, really is a "copyrightable" year that would be listed
    individually; and you make an explicit statement in your
    documentation about this usage.

(See http://www.gnu.org/licenses/gpl-howto.html for the full text.)

In the case of ImageJ, every year in the range is, and will continue to
be, a "copyrightable" year. The only issue is whether we have made "an
explicit statement" in our documentation. Unfortunately, the guide does
not explain any further what such a statement might look like. There are
thousands of projects on the web that use date ranges and it is
unambiguous what they mean, so I think we are safe with this practice.

Lastly, continuing to enumerate all the years individually will run out
of real estate on the image within a few years' time, whereas using a
date range will scale well into the foreseeable future.