Removed class to prevent display of modal dialog.

For Protege 5.0 beta, we are not offering the InstallAnywhere platform
independent installers as a method of download.  No longer want to
display the modal dialog that allows users to choose the InstallAnywhere
installer for their particular platform.
Updated button text.

Changed contents of span to say 5.0 beta instead of 4.3 in preparation
for our next Protege Desktop release.
Don't compute href anymore.

Clicking on the Download button used to bring up a modal dialog where
users could select an installer file for their platform.  No we're just
offering a ZIP file, so the href attribute is hard coded to link to
whatever ZIP file is the current version for Protege Desktop.
Removed "Other downloads" menu.

Replaced with direct link to wiki page that lists older versions of
Protege.  For Protege 5.0 beta, there will only be one option for
downloading (ZIP file).
Revert "Don't compute href anymore."

This reverts commit 9d351f219944932f8358b2c35737e74c91ad9593.
Modify href depending on platform.

For the Protege 5.0 beta distribution, we'll offer a ZIP file for
Windows and OS X, and a tar.gz file for Linux.  Need to modify the href
attribute to point to the appropriate file based on the end user's
operating system.
Updated links to point to 5.0.0 beta, build 10.
Added item to Documentation menu.

New item is a link to installation instructions for Protege 5.0 beta.