use Eclipse Juno as target platform

Note that Indigo does not run easily with Java 7 on Mac anyway, so going Juno is quite ok
Isabelle Product feature to package additional plugins for Isabelle/Eclipse standalone IDE product
plugin for Isabelle/Eclipse product branding
Isabelle/Eclipse product definition and launcher icons
intro artwork update
include product branding plugin in the feature
better Maven project name
a launch configuration to share with other developers testing Isabelle/Eclipse
using GIMP-generated icon (better transparency handling than bash `convert`)
using 8-bit icons with white background (looks better if 32-bit icons are not supported)
Merge branch 'ide-product'
note that Java 7 is required