Reduce the number of Bastion dependencies

[KPull]

I've cleaned up the code so that we can mark the following two dependencies as optional:

• JUnit 4
• JMustache

If the user wants to use these features with Bastion, they need to add them to their own POM file first (they're not pulled automatically with Bastion).

This fixes: #57.

[KPull]

I talked with @FrelliBB about this who suggested we split up the optional modules into their own Maven modules. This is actually the suggested way of doing things, with the advice written on the same page which explains 'Optional Dependencies': https://maven.apache.org/guides/introduction/introduction-to-optional-and-excludes-dependencies.html

We're going to try out how the whole structure will look like once we split everything up into dependencies.