Allows completion of local variable and function names.

Task-number: QTCREATORBUG-942
Reviewed-by: Roberto Raggi

Previously we just scanned every directory containing a qml file for
other qml files.

This makes import ".." work.

Reviewed-by: Erik Verbruggen

* Fill the snapshot with files that could be imported.
* Implement package imports.

* The qmldir file is not parsed yet.

Reviewed-by: Erik Verbruggen

* The "Script" type is now implicitly available without imports.
* No errors for bindings inside a Connections element.

Reviewed-by: Roberto Raggi

* For JS files: Add each Qml component that sources the file in a Script
  tag to the scope chain.
* For Qml components: Add each component that instantiates the component
  to the scope chain.
* Generate the full list of documents required for completion in a
  given file. Previously, files that included the file were missing.

There is no reason to store the Bind object in a QSharedPointer because the `binder' has the same
lifetime of its document.

Done-with: ckamm

* Support for lookup JS vs Qml
* Bind global variables.

Done-with: ckamm

Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

Done with: Erik

Enables completion for function declarations inside qml files.

Done-with: Christian Kamm