bitbake: toaster: improved Project models

bitbake: toaster: improved Project models

A layer may live in a subdirectory of a git repository,
so we add a field to track this setting in the Project layers.

We add the Project schedule_build function, which creates
a build request from the current project configuration.

We also fix an import problem with Projects in views.

(Bitbake rev: 1b5835e5d48cbfb7d38e38437c45d161052dfb37)

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