simplify configuration and improve UI Session handling implementation

[bicarbon8]

• consolidates aftconfig.json handling into the AftConfig class which can either read directly from your aftconfig.json file or from a passed in JsonObject and can use concrete configuration classes as interfaces for retrieving sections of the configuration making it easier to define individual plugin configuration
• changes plugin loading process to a single array of all plugins which are loaded at the start and are then filtered by type using comparison against their base class implementation to ensure they meet expected interface being requested
• removes defect plugin in favour of a combined TestExecutionPolicyPlugin which is responsible for determining if a particular test case should be run based on Test ID
• removes direct integrations with BrowserStack and Saucelabs in favour of a more flexible system that passes in unstructured options which can then be used as capabilities or remote options by selenium and webdriverio packages
• adds direct validator integration into jasmine and mocha reporters making it easier to skip tests that should not be run and to wrap tests in validator assertions