Hob: add Templates and Settings on image details screen

Hob: add Templates and Settings on image details screen

This patch is to add Templates and Settings tool buttons on the image
details screen, which makes things easier and simplier.

In order to fulfill that, the code splits the functions
show_load_template_dialog() and show_adv_settings_dialog() in builder.py
because they will possibly be called from different screens later.

[Yocto #2163]

(Bitbake rev: 29bea7b7076a7b74d36237da86a4eff6605d17ec)

Signed-off-by: Shane Wang <shane.wang@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>