Some minor feature additions

- Supports default redirect page after authorisation, if no config is set
  up
- Removes error messages if email credentials not set up
- Does not add subscription on new user signup if subscription is already
  present
- Flush response after message received and OK message sent, just in case
  it does not auto-flush. This should get the ack out quicker.
Customisable welcome card

Allow the user to create their own welcome card (the first card that is
posted to the user's timeline when they log into the glassware). To create
a custom card, the user should create a service called WelcomeService,
with a method

TimelineItem makeWelcomeCard()

This method should create and return a timeline item that will be posted
to the timeline by the authorisationService. If no such service or method
exists, the default "Welcome to APPNAME" card will be used. If a method
exists but does not return a TimelineItem, a runtime error will be
thrown
Added example project TellAJoke
Remove target directory from git
Support for image attachments

Added feature for rudimentary support of image attachments. If the user
performs a 'share' action on a card, and the card contains image
attachments, they are retrieved, and stored as a BufferedImage on the
params.attachments list passed to the messageHandlerService. Attachments
for all other actions are not yet supported, and behaviour when the
attachment is not an image (readable by javax.imageio.ImageIO) is not yet
specified.
Fix for authorisationService insertSubscription call and added icon for example app