Added mocking support for internal module methods, aliases, applications, filters, etc

Added mocking support for:
* internal module methods
* alias commands
* application commands
* filter commands

Added partial mocking support for:
* fully-qualified command names (fully qualified cmdlet invocations are not supported)
* external script commands
  The only supported scenarios are when the script is invoked using one of the following methods:

    scriptName.ps1

    & scriptName.ps1

    . scriptName.ps1

Added corresponding unit tests.