Create Dialog-Framework

[hohwille]

We need to create a dialog framework with the following features:

• history management (browser back and forward-button, bookmarking of dialog state)
• embedding (opening dialog opens parent dialog recursive and embedding into slot of parent dialog)
• code-splitting (prevent that client has to be loaded as single large BLOB at startup)
• simple access to current dialogs by type
• separate dialog and popup(-dialog)

[hohwille]

Except some few small fixes the design works like a charm from the start. Some little refactorings have been done to improve the usage of the framework from the users perspective. Two aspects are currently open:

• If a (main-)dialog is opened and it therefore opens its parent dialog and embeds itself into a slot of that dialog, there may be other "secondary" slots of the/a parent dialog that may need to be filled (e.g. navigation or side dialog). There (parent) dialog should be able to define which dialog is the default for a slot (potentially based on the DialogPlace to open). If that is not already set in the slot it should be done. Further the initial dialog may also trigger the opening of a sibling dialog for that slot via an explicit DialogPlace.
• The DialogControllerFactory currently creates all DialogControllers at once for simplicity. For GWT/Web clients this can prevent proper code-splitting. Therefore we need to rework on this.

[hohwille]

There has to be support for async usage. The dialog controller may need to invoke a service to decide for the slot to embed into. Some advanced use-case but definitely required.