In order to track the file where a configuration
variable was defined, this patch bring these changes:

* a new feature is defined in CookerFeatures, named
BASEDATASTORE_TRACKING. When a UI requests BASEDATASTORE_TRACKING,
the base variable definition are tracked when configuration
is parsed.

* getAllKeysWithFlags now includes variable history in the
data dump

* toaster_ui.py will record the operation, file path
and line number where the variable was changes

* toaster Simple UI will display the file path
and line number for Configuration page

There is a change in the models to accomodate the recording
of variable change history.

[YOCTO #5227]

(Bitbake rev: 78e58fed82f2a71f052485de0052d7b9cca53ffd)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>