Visualize item flags in QuickInspector's item tree

With this commit the item tree view in quickinspector visualizes item
flags, which are added in this commit as well. Item give some random,
but useful infos about an item, like is invisible, has active focus,
etc.
These infos are shown in the tooltip as well as by showing icons in
the tree view or changing the text color.
Moreover with this commit items that changed recently are highlighted
for a few seconds using a red text, animated to fade back to black.
QuickItemTree: Replace item widgets by a delegate.

In order to be able to animate the text color, the quick item tree had
a widget for each item in the tree view with the text and icons. This
has the consequence of huge widget trees, which results in very bad
performance. Now the same is done using a QItemDelegate.
Silence a few compiler warnings.
Quick item tree: Use QStyledItemDelegate.

Now the delegate is a QStyledItemDelegate instead of a QItemDelegate,
causing the background and stuff to be rendered according to the
style, instead of just painting a blue rectangle.
Quick inspector: Correctly update item tree flags.

Now flags are updated recursively for all children, if the position of
an item changes.
QuickItemTree: Skip root item in out-of-view check

In Qt 5.2 the root item of a scene has a size of 0. This caused all
items to be considered to be out of view. Now the root item's (only)
child (the outer-most item, that is explicitly defined in QML), which
has a correct size is treated as the scene size, thus now the check
is working correctly with Qt 5.2, as well.
Add LoadingState role to remote model.

This role allows the view to check, whether the data is being loaded
initially, is outdated or current.
This allows to optimize the visualization of the data in regard to its
loading state.
Quick item tree: No animation on initial load.

This commit removes the animation, where the text in the item tree
view fades from red to black, for the initial load.
Prior to this change on the initial load all items would be red,
fading out together to black. Now the animation happens only when the
data actually changed. This is done using the loading state
information from the remote model.