[qmf] When messageListModel limit changes add more messages to model instead of full refresh.
[qmf] Remove messages in excess when model limit decreases

Remove messages in excess when model limit decreases, if limit becomes
zero a full model reset is performed.
[qmf] Remove exceeding elements in the message model after inserting new ones

New messages can be inserted anywhere in the model, when the limit
is exceeded we remove the elements in excess, i.e the trailing ones,
instead of stopping the insertion of new elements, that can have a smaller index
than the existent ones.
Merge pull request #57 from nemomobile-packages/listLimits

[qmf] When messageListModel limit changes add more messages to model ins...