Debugger: Do not soft-assert on missing tool chain

Not having a tool chain is actually allowed, so do not soft-assert
for that.

Change-Id: Ia913fa271a1f1e299451e9fabd4ed6bcfb32f043
Reviewed-by: hjk <hjk121@nokiamail.com>
Gerrit: Refactor preparing the introduction of a hierarchical model.

Change model and dialog methods to use QModelIndex and remove
obsolete methods. Split out method to populate a list of standard items
from a change. Change GerritModel::itemForId() to recurse
over the tree.

Change-Id: I9393f498ffbdf63ba3ad78146d041bcda3835527
Reviewed-by: Orgad Shaneh <orgads@gmail.com>