Create stable installers and "portable app" bundle

[ctrueden]

The Downloads page currently has two major download sections:

• A build of ImageJ2 from the master branch.
• Bundles of Fiji from its master branch.

In the case of ImageJ2, we also cut release versions which are uploaded to the core ImageJ update site (i.e., pushed to users).

This issue entails the following work:

• [ ] The main download of ImageJ from the downloads page should match the released version of ImageJ2 (not the tip of the master branch).
• [ ] There should be friendly installers for Windows (.exe or .msi) and OS X (.dmg). Fiji already builds an OS X .dmg, which we can generalize (though see fiji/fiji#106). But for Windows an installer really needed—see #72 for details.
• [ ] There should be a "portable app" bundle of ImageJ that includes a generic shell script launcher and no JREs.
• [ ] Unify the ImageJ and Fiji bundle generation of Jenkins to reuse logic as appropriate.

[ctrueden]

For OS X, we should look at industry standard app bundlers if we can find anything decent. Here are some candidates:

• https://bitbucket.org/infinitekind/appbundler
• https://github.com/federkasten/appbundle-maven-plugin

Note that the Mojo osxappbundle Maven plugin works with Apple Java and is incompatible with Oracle Java 7+.

See also this comprehensive article:

• http://docs.oracle.com/javase/8/docs/technotes/guides/deploy/self-contained-packaging.html

[hinerm]

@ctrueden

See also this comprehensive article:

    http://docs.oracle.com/javase/8/docs/technotes/guides/deploy/self-contained-packaging.html

This is essentially the same JavaFX doc I found. All the JavaFX configuration I've seen is Ant and NetBeans based, but it does look like there is a maven wrapper as well.