TpContact should have helper API to set alias

Submitted by Xavier Claessens @xclaesse

Assigned to Telepathy bugs list

Link to original bug (#28037)

Description

In most cases, setting the alias is done only for 1 contact. Lowlevel API is a pain to use because it needs creating hashtable, etc...

I suggest adding simple API on TpContact:

void tp_contact_set_alias_async (TpContact *self, const gchar *new_alias, GAsyncReadyCallback callback, gpointer user_data);

gboolean tp_contact_set_alias_finish (TpContact *self, GAsyncResult *result, GError **error);