Make $scope.searchOwner undefined before it had a chance to be
initialised, this to comply with hb-choose-actor controller new
requirement in order to distinguish "initialised empty" from 
"non intialised" state in asynchronous loading context.
Comment.
Changed null string to null reference initial value for prestationGroup
local variable.
Added editTransaction() mode and associated button switching back from
reallocateTransaction mode. 
Moved from evil != == operators to their safer twins !== ===
Fixed $scope.searchOwner value in edit mode. It must be undefined.
Major refactoring solving actor selection initialisation where 
specified hb-choose-actor default value must not override 
existing actor model value set by the context. For instance 
owner actor defined by PRESTATION context while creating a new
TRANSACTION from PRESTATION.
Code clean up.
Deal correctly with setDefaultActorByName procedure waiting for actors
list loading to complete if necessary.