We extract the functionality we added to v-play
for being able to just attach a page to the navigation
stack into its own component.

// Github issue #82

With the food and shopping menu entries in place,
on SailfishOS the menu behaves weirdly: The shopping list
gets pushed as a new page onto the stack of the food list
(without a 'PullDownMenu', which is still on the food list page).

We therefore create the entity of an 'ActionMenuItem',
which closely resembles Sailfish's PullDownMenu's 'MenuItem':
It has a 'clicked' signal, which you can connect to
for triggering some action when the menu item was clicked.

Currently, the 'ActionMenu' item uses the page component that
has been assigned to the 'initialPage' property of the
'ApplicationWindow'.

The 'NavigationMenu' abstraction on Sailfish is adapted in a
way that the menu automatically assigns itself to the first
page of Sailfish's global 'pageStack' (if it has a valid
'flickable' the 'PullDownMenu' can be attached to).

(avoids unnecessary indirection).

// Github issue #82

as nice as it is --- but unfortunately it is
overkill for our use case.

// Github issue #82

(vestige from debugging).

With Github issue #82 the bug of the virtual keyboard
loosing the focus was temporarily re-introduced.

// Github issue #82

for both V-Play and Sailfish: This allows us
to put the search bar in the header of the flickable
on SailfishOS, but have it as a static item on top
of the venue list on V-Play.

Closes #84

// Github issue #82

// Github issue #82

and don't implicitly use app.initialPage

// Github issue #82