ExecTree initial commit
add xml import/export functionality
add job file validation
Work in progress: Queueing logic
Adding job execution code and tests.
Add archive browsing.
implement subtree support

A job can now execute a tree instead of a script
Remove notion of job nature & simplify events.

Have one event per possible job state. Let even subscribers just choose
the event they are interested in.
Implement subtree iteration.
Implement argument handling on tree itreation

Also, add functionality to specify where to write log files.
Draw itterated subtrees in graph.
Add test for undefined job, setup py.
Added arborescent graph drawing.
Add script parser which converts to exectree

Change-Id: I9dba97db2272669a2ac28a46847a787233f48c88
custom args, json, undefined job

Implemented aformentioned features. Fixed some DAG validation
performance related bugs.

No doubt, some test need to be expanded.
Add resource management to execTree
Implement re-run & unit test for it
Resolve resource related bug.

Add __str__ methods to ExecTree Classes.
work in progress
Fixes link creation in graph.

pydot doesn't properly handle href attrib, using kludgy way of passing
it in at instantiation of node.