Merge pull request #102 from cs2103aug2014-w13-1c/jin/gui

Created a static Logger instance in Main
Merge pull request #103 from cs2103aug2014-w13-1c/jin/gui

Refactored logging to make use of a singleton service class called LoggingService.
removed unused imports in RootViewController and deleted unused InputField.fxml
started logging inputfield changed inputs and instant search queries using LoggingService
Merge pull request #106 from cs2103aug2014-w13-1c/jin/gui

Made a minor change to LoggingService, but it doesn't affect current references to it.
created InvalidInputException class to handle invalid inputs
Implemented InvalidInputException for InputField when encountering an empty command
added a few assertions in InputFieldController
Merge remote-tracking branch 'origin/staging' into jolly/gui
Merge remote-tracking branch 'origin/staging' into jin/testfx