Release mrv2 v0.6.3 · ggarra13/mrv2

v0.6.3

Added a python plug-in system which is now documented in the
Help->Documentation. The environment variable used to look up plug-ins is:

MRV2_PYTHON_PLUGINS

It is a list of colon (Linux or macOS) or semi-colon (Windows) paths.
Plug-ins are defined, like:
```
class Plugin:
    def hello(self):
        print("Hello from plug-in!")

    def menus(self):
        menus = { ("New Menu/Hello", self.hello) }
        return menus
```
Added a mrv2_hello.py plug-in for demo purposes.
Fixed a bug in the log panel appearing compressed on start up when docked.
Allowed creation of .otio files of a single clip in Playlist Panel.
Fixed scratched frames showing up on .otio files with gaps in them.
Fixed a huge bug of preferences not hiding the different bars anymore (regression in
v0.6.2).