[libcontacts] Allow online accounts to be imported for demo purposes

Although they won't work correctly, allow IM accounts to be imported.
Merge pull request #61 from matthewvogt/demo-im-accounts

[libcontacts] Allow online accounts to be imported for demo purposes
[libcontacts] Track whether contacts have valid IM accounts

Although QContactStatusFlags reports whether an account has any IM
accounts configured, we need to also know whether any of those accounts
are connected to valid telepathy accounts.
[libcontacts] Update changed contacts progressively

Update contacts in small batches to prevent blocking the UI thread.
[libcontacts] Append contacts to model progressively

Avoid blocking the UI thread when the cache is populated after process
startup.
[libcontacts] Do not emit change notifications during initial contact insert

When a contact is first loaded into the cache, no listener can yet be
interested in changes to that contact.
[libcontacts] Use backend display label in preference to address detail

When generating a display label for a contact, use the display label
provided by the backend in preference to any of the direct address
elements in the contact.
[libcontacts] Update modified contacts individually rather than in batches

Processing even a single changed contact can consume all the available
time between UI frames, if it causes QML bindings to be re-evaluated.
Merge pull request #57 from matthewvogt/progressive-indexing

Progressively update/append contacts to the cache to avoid blocking UI
Merge pull request #63 from matthewvogt/display-label-precedence

[libcontacts] Use backend display label in preference to address detail
[libcontacts] Handle presence updates independently

qtcontacts-sqlite allows clients to handle presence change notifications
separately from other contact change notifications.
[libcontacts] Optimize fetching of presence updates
[libcontacts] Remove sorting from incidental fetch queries

The order of contact processing in update queries has no relevance.
[libcontacts] Do not sort refetch contact details

Sorting has no effect after the models are initially populated.
[libcontacts] Stop pretending that we support multiple engines

libcontacts will only work correctly with the qtcontacts-sqlite
contact manager engine; remove the use of the NEMO_CONTACT_MANAGER
environment variable from qt4 code.
Merge pull request #59 from matthewvogt/presence-updates

[libcontacts] Handle presence updates independently
Update dependency versions
[libcontacts] Defer fetching changed contacts when display is off

Do not respond immediately to contact change notifications when the
display is turned off.  Instead, defer fetching until the display
is re-enabled.
Merge pull request #64 from matthewvogt/suppress-retrieval

[libcontacts] Defer fetching changed contacts when display is off
Merge pull request #62 from matthewvogt/valid-im

[libcontacts] Track whether contacts have valid IM accounts