Method call on `this` in the context of causality analysis

[ptal]

A problem occurs with method calls such as this.m() since m has accessed to every field of this (see #2).
To allow non-static methods in a spacetime module, we can etiher:

1. Analyse the Java method to check for read and write accesses (seems very complex since we must parse and understand the full Java syntax).
2. Annotate the call on this with the permissions of the variables accessed.
3. Allow possible causality holes when calling external functions (i.e. Java methods).