hob: create a base hob image used to create custom images

hob: create a base hob image used to create custom images

In order to remove hob-image.bb from meta-hob, a hob-image.bb should
be created somewhere in the build directory. I've saved it in build/recipes/images
directory, and moved the templates to recipes/images/custom (here are those
templates saved by the user).
The image is created when hob starts. Also it appends to BBFILES the directory
where it is created.

Removed images directory from meta-hob.

[YOCTO #5118]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>