Avalon-core

Minor Improvements
* Avoid `keyPressEvent` interfering other widgets (529)
* Fixed 508, sorting creator plugins by label (530)
* Fixed 536, *Scene Inventory* now can select entire rows from action (537)
* Implemented 544, *Workfiles* now closes itself on scene open (545)
* Added `QWidget.activateWindow()` call on `{tool}.show()` to guarantee shown on launch (522)

Major Changes
* :sparkles: Avalon Loader load subset with options (**482**, 518, 521)
* :rocket: Fixed issues in Maya 2020 (**486**, 488)
* :muscle: Refactored Avalon config import method into `lib.find_submodule` (**501**, 515)

Minor Improvements
* Fixed Avalon tools not parenting in main window (472)
* Fixed Loader in Houdini 18 returning version number as 'long' not 'int' (479)
* Improved fps mapping in Maya (475)
* Improved log message for no creator plugin been found (490)
* Tiny Houdini `lib.lsattr` improvement (491)
* Fixed OptionalMenu highlighting in Loader (521)
* Fixed missing key `AVALON_HIERARCHY` in Avalon Session (525)
* Tiny Avalon GUI styling improvement (528)

Nuke Integration :construction:
The Avalon-Nuke integration is still in developement here, there's an PR 504 which is built on top of these changes and waiting for more tests and feedbacks. Welcome to give it a go !

* Re-implemented Nuke `imprint` (473)
* Implemented Nuke's `lib.read` (476)
* Porting 438 (484)

Fix Avalon-Nuke implementation

See 471 for detail.

* Optimized Maya host.ls() method - 456

Instead of using `avalon.maya.lib.lsattr` which scanning all nodes, implemented an internal method specifically for iterating only `objectSet` nodes for listing containers. The speed is about 5 times faster.

* Removed schema validation when parsing containers - 458

The container data schema validation was dragging the process when the scene has lots of subset loaded. Removing it for performance.
**The flag `validate=True` in `pipeline.parse_container` has been removed.**

* Fix `avalon.lib.launch()` for non-Windows platform - 459

The `subprocess.Popen` flag `creationflags` only works on Windows, and cause error on non-Windows platform.

* Improve Python 3 compatibility - 462, 464, 469

Improve for host which using Python 3+, e.g. Blender.

* Fix Workfiles app for working in Blender - 465

This is a must for upcoming Avalon-Blender implementation. :rocket:

* Minor fix
- Fix tools debug mode - 470

* Exposed the "loader" column in Scene Inventory : 455
* Made the "No Task" entry clearly distinct from actual tasks by its icon : 452
* Fixed context manager allowing to switch to 'No Task' : 451
* Fixed `QPushButton::menu-indicator` being cut off : 450

* Resolved 246 : New document schema to store `families` in subset

If you want to adopt this, the Pyblish Integrator plugin which responsible to write `subset` and `version` into the database, require to update the document schema name.

And here's the simplest principle that worth to follow:
* If subset already exists, do not use new schema on next version.
* If subset will be created on integration, do use the new schema on both subset and version.

Backward compatible, see 443 for detail.

* Resolved 407 : Refactor Work Files API

* Renamed `workio.open` to `workio.open_file` in each host.
* Renamed `workio.save` to `workio.save_file` in each host.

This is backward compatible, see 449 for detail.

* Optimized `AssetModel`

The launch time of Loader tool and Project Manager has been decreased tremendously.
See 447 for detail.

* Resolved 179, 289, 445 : Improved Creator tool

* Better visual feedback and status message from subset name input field
* Validate inputted subset name immediately with GUI feedback
* Fixed asset name validation bug