bitbake: toaster: create models for bldcontrol and enable it

bitbake: toaster: create models for bldcontrol and enable it

We create the model classes that store information
about triggering builds, and the available build
environments.

We add a fixture with a default build environment
for build control, using a "build/" directory under
the poky checkout directory.

We enable the bldcontrol in toaster starting script
and in the toaster settings as to allow the actual database
to be kept in sync with the source code.

(Bitbake rev: d4bfe9059f765f11244b97e324c0131f32f8e400)

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