Allow modules to load instance assets.

[flo]

This change probably fixes the instanced asset creation from issue #62

I am not sure how to configure my terasology to use the gestalt source version.

I also didn't find a proper 5.1 branch to make this PR to as Terasology still uses 5.1.2. The commit in this PR is based on the latest 5.1.3-SNAPSHOT commit.

It would be great, if you @immortius could explain me how you test a gestalt change with Terasology without building new version. Ideally this should also be documented so I created an issue for this: MovingBlocks/Terasology#3027

[flo]

This fix is btw. needed by the Scenario module. It uses it to allow you to allow you to define "event -> actions" logic ingame without programming knowledge. For this actions you can define recursivly expressions for which it is necessary to display the same dialog multiple times.

The GSOc student @ThompsonTyler (alias cata) works on that module and @nihal111 plans to use it for his gsoc project too.

[flo]

Ok was able to test and I can confirm that the PR indeed did fix the issue.

To test I build gestalt with "./gradlew install" and then changed in engine/build.gradle:

-    compile group: 'org.terasology', name: 'gestalt-module', version: '5.1.2'
-    compile group: 'org.terasology', name: 'gestalt-asset-core', version: '5.1.2'
+    compile group: 'org.terasology', name: 'gestalt-module', version: '5.1.3-SNAPSHOT'
+    compile group: 'org.terasology', name: 'gestalt-asset-core', version: '5.1.3-SNAPSHOT'

[Cervator]

Branching stuff is all set now :-)

I might simply make a new Gestalt job in Jenkins purely to build a v5.1.3

[immortius]

This is a reasonable change. One request - I would like the error handling to be in line with #reload - it should get the cause from the privileged exception.

[Cervator]

So essentially replace the one logger line with something like this?

logger.error("Failed to register asset '{}'", asset.getUrn().getInstanceUrn(), e.getCause());

[flo]

@immortius done