[bugfix] Prevent crash if SNI is destroyed and SNMI being destroyed too

This commit prevents a crash if SNI is destroyed where SNMI is
destroyed too. If we call QALM::endRemoveRows() while the view
is being destroyed, it might lead to some double free (item models
are being removed first by the view and again by the model). If we
don't clean when deleting the SNI, we cover most user-case and
prevent this crash.

The only issue that can happen is that we keep the SNMI and
destroys the SNI. Then, data in the SNMI would stay. It is
not really nice, but shold be so rare that we can discard
this case.
[bugfix] Fixes segmentation fault

This commit partially reverts the previous commit.
Now instead of clearing data from the models using
clean(), it just clear the list of data, without
calling beginRemoveRows and endRemoveRows.
Initial work for new NQPS

New NQPS will provide a more extensible and
stable API for interaction with social network.

API changes:
- filters is no longer a list and is renamed filter
- populate/repopulate no longer exists, and are renamed load
- filter is used in IdentifiableContentItem based items to load items
- actions like like, comment are disabled for the moment
- Filter based class have been revisited.

Internal changes
- Cache removed for the moment
- Private and friends classes are removed, and public methods
  are used instead
- Filter are given more responsibilities (perform a network load,
  set data to an item etc.)
- Centralization of roles: items / model for displaying data,
  filters for performing actions, SocialNetworkInterface based
  classes for interacting with social networks
More work

Added support for models load next / previous,
added offset for Facebook model filter.
Minor fixes

These fixes gives more information to the developer if
he / she only listens to statusChanged signals. Other
fields (like have next / previous and errorMessage)
are updated before, so updated values are available.
Minor fix
Enabled sorters
Fixed loading next / previous when not allowed to do so
Added protected D-pointer constructor
Readded support for actions

- Actions are controlled from SocialNetworkInterface
- Implemented objects usually call run<ActionName>
- These actions need to be implemented in subclasses of
  SocialNetworkInterfacePrivate, as static methods.
- Twitter not enabled yet
Bugfixed Post interface

There were two bugs, leading to setting "to" to
some invalid value.