HaikuDepot : Refactor Screenshots

Rework the way in which the application deals
with screenshots so that there is a repository
of screenshots that is referenced from
identifiers on the package model and not that
the screenshot bitmaps are stored with the
model and not cleaned up.

Change-Id: I632def96852a518b3f6b1c8b81909de117bbbc54
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7296
Reviewed-by: Andrew Lindesay <apl@lindesay.co.nz>

HaikuDepot : Break Out Pkg Model

The data model for packages contains a number
of components which all reside in a single
source header and implementation file making
maintenance and modifications difficult. This
change will break the sub-models out into
separate files without making any functional
changes.

Change-Id: I9c2557bc1e5a33661145c55290a0baad4084fd49
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7181
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>