Simplify dx find jobs --trees

Conflicts:
	src/python/dxpy/scripts/dx.py
New API methods findExecutions, findAnalyses
High-level wrappers for findExecutions
Begin dxclient integration of findExecutions
Begin fixes to rendering of analyses in pretty-printed output
dx find analyses is not compatible with --trees
Remove trees format and substitute with repeat call
Debugging improvements
Remove --summary argument (subset of fd5f8234 for merging)