Adding task worklets, a worklet gallery, and related changes.

Add task worklets and a task gallery

There are times when an user will need to interactively extend a task workflow by adding new tasks or a pre-connected set of tasks to the existing workflow, including new dependencies and adaptors. To provide this functionality, SMTK adds the concept of a worklet. A worklet is an object representing a set of tasks created to reuse a set of workflow logic in multiple workflows. In SMTK, a worklet is represented as a component of a project and is managed by a project's task-manager in a collection of worklets known as the "gallery."

This change also

• makes task::Adaptor inherit resource::Component
• refactors task events and their observers to occur during observation of operation results (rather than spontaneously, since now that tasks, adaptors, and worklets are components, that would force these events to happen during operations).
• adds a simple worklet example in the data/projects directory called SimpleWorkletExample.
• moves the math_op.py plugin (which is used by multiple projects) to now be under data/operations
• adds an EmplaceWorklet operation to instantiate tasks, adaptors, and dependencies from a worklet into its task manager.
• adds a RenameTask operation that allows users to change task names and a context-menu that runs this operation.
• adds the qtWorkletModel, qtWorkletPalette, and pqSMTKWorkletPanel GUI extensions to allow users to drag worklets into the nodal task user interface (and thus run EmplaceWorklet).
• removes the task-node UI-state that previously stored the (x,y)-locations of tasks in the nodal task UI (this will be replaced with a separate facility for storing the information without the overhead and timers of the removed approach).
• fixes an issue when creating instances of the PyOperation class (the base for all operations written in Python) from a non-GUI thread by providing an override for the create method that runs Python code in the GUI thread.
• Added the concept of UIElementState so that UI Elements such as the pqSMTKTaskPanel can save and restore Task Node locations when being rendered.
• Added a map of UIElementStates to the View Manager so that operations can set and access the current configurations of the UIElementStates
• Task Node locations are now stored in their own JSON element in a Project's JSON. All UI state information should now be stored under the "ui-state" key.