Add BSD license block and CodePlex copyright to each source file

See discussion in #10.
Drop MIT license; move BSD license to root directory

All OpenSeadragon contributors have granted their permission for this
relicensing in #58.

Drop copyright statements for Ian Gilman and Christopher Thatcher as
they requested in #10.

Revert CodePlex Foundation copyright date to 2009 pursuant to discussion
in #10.
Clean up LICENSE.txt formatting
Add MIT license blocks to src/openseadragon.js

for code taken from jQuery and from mattsnider.com.

Ideally we'd keep the MIT-licensed helper code in a separate file,
but it proved difficult to extricate from the rest of openseadragon.js.

Also remove comment about plagiarism.  It's not plagiarism if it's
attributed and properly licensed.
Add copyright statement to LICENSE.txt

The license speaks of "the above copyright notice", so it would behoove
us to have one.
Add "OpenSeadragon contributors" copyright statement

The license text will be provided on the website, etc., and it seems
strange to list no copyright date newer than the original CodePlex
copyright from the AJAX Control Toolkit.  Add a blanket copyright
statement for contributions to the OpenSeadragon project, stating that
copyright is held by the authors of each contribution.  This blanket
statement is not intended to preclude individual contributors from
attaching their own copyright statements to their modifications.
Fix inherited error in clause 3 of LICENSE file

The original AJAX Control Toolkit license prohibited the name of the
CodePlex Foundation from being used to endorse/promote derived products.
We need to preserve this requirement.  This was already done in the .js
header blocks, and should have been done in LICENSE.txt in a7c96c56 but
was missed.

Original discussion in #10.  Permission for the license change was given
by all existing contributors in #58.
Add license link to header of minified JS
Document New BSD license on seajax-utils OSM/TMS code

@rsimon has given permission in #58 for the OSM/TMS code that originated
in seajax-utils to be released under the New BSD license.
Document MIT license on John Dyer's fullscreen code

See #81.
Include 2010 in "OpenSeadragon contributors" copyright dates

This Git repository starts in 2011, but the CodePlex Mercurial repository
has commits from 2010.
Move project URL above license URL in minified header
Replace GitHub issue numbers with full URLs
Add file-specific descriptions to file headers
Document New BSD license on @jpstroop's IIIF code
Merge pull request #89 from bgilbert/license

Revert to original New BSD license; clean up license declarations