[FEATURE] Add configuration option for notification transmission channel

Add configuration value hipChatNotificationTransport to the extension
configuration to provide an option to select the desired notification
transport: both (email and HipChat message), HipChat message only,
email only (defaults to email and HipChat).

Further code cleanup and unification (CGL, order).
[TASK] Update ChangeLog and ReadMe to reflect latest changes
[TASK] Change format of ChangeLog to markdown
[TASK] Release HipChat 1.1.1 to TER