- startup, login and onboarding modules merged into the single one
- `State` class introduced which is the base class for all states, every state
determines what is the next state in each of 3 possible actions, and what
is the previous state, if it has previous state
- `StateWrapper` class is introduced as a convenient way to expose
`State`'s props and deal with them on the qml side
- startup module maintains states as a linked list and there are few convenient
methods to move through the list `onBackActionClicked`, `onNextPrimaryActionClicked`
`onNextSecondaryActionClicked`, `onNextTertiaryActionClicked`
- redundant code removed
Fixes: #6473
Michał Cieślak
Sale Djenic
Khushboo Mehta