Introduce QDict

QDict is a high-level dictionary data type that can be used to store a
collection of QObjects. A unique key is associated with only one
QObject.

The following functions are available:

- qdict_new()    Create a new QDict
- qdict_put()    Add a new 'key:object' pair
- qdict_get()    Get the QObject of a given key
- qdict_del()    Delete a 'key:object' pair
- qdict_size()   Return the size of the dictionary
- qdict_haskey() Check if a given 'key' exists

Some high-level helpers to operate on QStrings and QInts objects
are also provided.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
