[BLUEJ-1292] Memory leak of old projects

When you close a project in BlueJ, it is not currently being garbage-collected as it should be. This could be for multiple reasons, but one is definitely that open editors listen to the central editor font size property, but never remove the listener. This means all editors are retained in memory, which in turn retains all projects.

We should use a profiler to find all such reasons that old projects are retained after the user has closed them, and fix them (e.g. remove listeners, or use weak references).

Issue metadata

Issue type: Bug
Priority: Medium