Don't rewrite icons when launching from within another application

[hinerm]

We received a report in the testing of ImageJ-MATLAB that launching from within MATLAB can replace the MATLAB icon with a Fiji icon.

I am hazy on the details but I thought the aggressive icon rewriting was a fix for OSX? I wasn't able to reproduce the issue personally on Ubuntu 14.04.

That said, if we can reproduce and isolate the issue, it would be great to be able to check if we're being called from another app or not, and avoid rewriting the icon in the former case.

[ctrueden]

This might be moot after we finally switch to JavaFX deployment... but definitely agreed that we should not be rewriting icons. What I would like to do long-term for ImageJ2 et. al is for each major update site to have the ability to add a little icon, which appears in the corner of the ImageJ splash screen (but not the application icon!). That way, everyone can see that A) it is still ImageJ; but B) they have such-and-such plugin suite turned on. Shiny.

[ctrueden]

We are switching the Fiji launcher to a new one we made called Jaunch. It does not have this problem, because it does not set the icon. It actually needs to set the icon in some cases (apposed/jaunch#31)—we should avoid reintroducing this bug when we implement that feature.