Removed biggest memory sieve - Finder (mostly fixes #385)

By some weird reason, Finder eats memory like crazy. Removed it in favour of iterators. This
also eliminated big dependency from the core.
Sort feature paths before testing them
Simplified FilesystemFeatureLocator::findFeatureFiles
Anchored the end of the regex matching the feature paths
Made the priority optional for all tags sorted by the ServiceProcessor

If the tag does not define a priority, it will be set to 0 by default.
Removed code duplication
Merge pull request #393 from WouterJ/improvements

Removed some code duplication
Merge pull request #391 from stof/optional_priority

Made the priority optional for all tags sorted by the ServiceProcessor
Merge pull request #387 from Behat/performace/finder-removal

Removed biggest memory sieve - Finder
Simplified the implementation of Scenario listeners

ExampleTested now uses getScenario to return its ExampleNode (implementing
ScenarioInterface), like ScenarioTested, simplifying the implementation of
listener running for each scenario. They can depend on
AbstractScenarioTested without doing instanceof checks to get the
scenario.
Simplified the ContextInitializer interface

The supportsContext method has been removed. All initializers are called
for each context. They should return early if they don't support it.
Added a method to access the StepTestResult exception easily

This allows getting the exception without worrying which part of the step
testing failed.
Merge pull request #400 from stof/scenario_events

Simplified the implementation of Scenario listeners
Merge pull request #401 from stof/simplify_context_initializer

Simplified the ContextInitializer interface
Added access to the Suite in the ContextClassGenerator
Replaced the GherkinSuite by a GenericSuite in Testwork

The Suite implementation was not tied to Gherkin at all.
Merge pull request #404 from stof/improve_class_generator

Added access to the Suite in the ContextClassGenerator
Merge pull request #405 from stof/generic_suite

Replaced the GherkinSuite by a GenericSuite in Testwork
Merge pull request #403 from stof/test_result_exception

Added a method to access the StepTestResult exception easily
Removed the concept of suite parameters from Testwork

Context parameters passed to the context constructor are now stored as a
setting among others and is specific to Behat.