Add standard dialogues backend independant

[jecisc]

Currently, a lot of tools are using UIManager to pop dialogues to the user.

I think (and esteban agree) that we should have an equivalent not bound to Morphic in Spec.

Esteban thinks it should be the application that should provide such dialogues.

We can think of

• A dialogue asking a question with 2 buttons
• A dialogue asking a question with an input text
• Idem with an input password

[pavel-krivanek]

there is a versatile dialog as a starting building block for that