2020 September 30th - Pitivi 2020.09

This release includes lots of new features, originating from GSoC
internships, from University of Nebraska-Lincoln's Soft-261 class
Spring 2020 and from individual contributors.

 * A plugin system allows extending the Pitivi functionality medium-term, targeted for teams of editors.
 * A developer console plugin allows interacting with the project in a Python console.
 * Custom UI replaces the automatically generated UI for a handful of effects.
 * Easy Ken-Burns effect.

 * The new Greeter perspective replaces the Welcome wizard dialog and allows a slick selection of a recently opened project.
 * When being resized, the Viewer shows the percent of the actual widget size in relation to the project video size.
 * The Viewer size snaps at 50% when being resized.
 * Scaled proxies if optimized media is too much for your machine.

 * Timeline markers.
 * Support for nested timelines by importing entire XGES files as a clip.
 * The Effects Library has been redesigned to allow quick access to effects.
 * Ability to favorite effects in the Effects Library.
 * Improved workflow for adding effects.
 * The refreshed clip effects UI allows working on multiple effects at a time.

 * Refactored Media Library using same logic for different view modes.
 * Refactored Render Dialog UI to avoid overwhelming people. Tell us what you think about it.

 * Restoring the editing state when reopening a project.
 * Safe areas visualization in the Viewer.
 * Easy alignment for video clips.
 * Composition guidelines in the Viewer.
 * Solid color clips.
 * Ability to mute or hide an entire layer.

 * Interactive intro so newcomers get familiar with the names of the UI elements.
 * The action search is a shortcut to everything possible in the timeline, if you can find it. Press "/".
 * New keyboard shortcuts for pros.