refactor(Constants): change class to enum

change to Constants class into an enum

Closes #5
refactor(OsgiScriptingEngines): remove second constructor

remove second constructor, which takes ScriptEngineManager, because the
class cannot work without ScriptBindingsFactory

Closes #10
refactor(Extender): move resolveScriptEngine method

move ResolveScriptEngine method from Extender to OsgiScriptingEngines
because it was the only class that called the method
move tests for that method into OsgiScriptingEnginesTest class
also remove Logger and getBundleContext from Extender because they
aren't needed any more

Closes #12
chore: remove everything related to BARs

remove BarDeploymentListener, BarTransformer and BarURLHandler and tests