Gradle Plugin / dump plugin with jre dependency

[Felix Natter]

Dear snapcraft experts,

I am creating a simple snap for a java application:

BTW: My original post is here:
http://askubuntu.com/questions/865090/simple-java-snap-with-jre-dependency

name: freeplane-snap
version: 1.5.18-1
summary: Java program for working with Mind Maps
description: ...
confinement: devmode
grade: stable

apps:
  freeplane-snap:
    command: ./freeplane.sh

parts:
  main:
    plugin: dump
    source: freeplane-1.5.18/
    stage-packages: [openjdk-8-jre]
    filesets:
      mybuild:
        - "*"
    stage:
      - $mybuild
    snap:
      - $mybuild

Freeplane uses a gradle build system, but the snapcraft gradle plugin is
not powerful enough (expects "gradlew" to be there and not "gradle", and
is used for single jar projects, i.e. always with 'jar' option). Where
can I submit feature requests / patches for this?

So I am using the project's binary distribution (unzipped to
./freeplane-1.5.18) with the 'dump' plugin, which works well. However,
since I'm not using a java build system, the jre is missing in the snap
(when running "freeplane-snap" I get an error that the JDK cannot be
found, NOT when running freeplane.sh directly). I tried to add it with
'stage-packages: [openjdk-8-jre]' but this did not help.

Could you please tell me how to add the jre to the mix?

One more question: Hearing about this containment stuff, is it
possible/feasible (using plugs?) to to create a desktop application that
can read and write (mind maps) from/to everywhere, just like a normal
.deb? (like plugs: [network, home, tmp]?)
I also need to install the desktop file and mime type mappings to
/usr/share/... --> I assume I can do this with separate parts?

Many Thanks and Best Regards,
-- 
Felix Natter