THUCYDIDES-160: add ClassFinder tests for classes located in JAR files

When they are run from an IDE like IntelliJ, the tests that use a maven
dependency do not test finding classes that are packaged in a JAR file.

This is because IntelliJ will setup the dependencies so that one module
depends on another module's .class files directly. This way, the IDE
does not have to waste time to package classes to jar files, and the
development is faster.
THUCYDIDES-160: tweaked build so that ClassFinder tests will fail if it doesn't properly handle whitespaces in directory paths
THUCYDIDES-160: fix issue

This commit fixes the loading of classes from jar files or file-system
directories, when the path contains characters which need to be
URL-encoded (e.g. the space character).

The existing code was taking only the space character into
consideration, whereas this commit fixes the issue in all situations:
every time the path contains characters that need to be URL-encoded.