Previously, preserved content was shown unexpectedly after its naviframe
item was popped because the preserved content was not removed but was
unset from its naviframe item.
Since popped naviframe item becomes hidden on the screen, the preserved
content of the popped naviframe item should become hidden by default as
well.
This touches Edje and also Elementary where part names are used.
This commit blew up in size since now all content part APIs
(get, set, unset) require to use Efl.Part instead.
This is a big refactoring commit, but no logic should
have been changed. Fingers crossed.
This removes Efl.Pack_Named which had a terrible name,
removes Elm.Container which should have been renamed
Efl.Ui.Container anyway, and introduces an interface
Efl.Container instead.
The hierarchy tree is now changed as objects don't inherit
from Efl.Container (it's an interface, not a regular class)
but only implement it. Obviously it is very easy to
reintroduce an Efl.Ui.Container parent class if we need it,
but I guess it should have some actual logic. It's basically
part of what Elm.Widget already does.
Some function names have been modified to look better in C
with the efl_content prefix.
@feature