Editor v3.11.1

[MichaelAldrich]

This is a re-deploy of 3.11 to fix our build pipelines, it's changelog is below :)

Additions:

+ Layer locking.
+ Added nxt-core version floor.
+ Added options menu.
+ Added user pref/action for toggling error "ding" sound.

Changes:

* Added model handling for GraphExit exception.
* Bug fix: Prevent exec cycles when setting node exec in.
* Slightly rounded node corners.
* Bug fix: Travis job was cloning nxt-core instead of letting nxt-editor find the version it needs on PyPi.
* Removed old test code - fixes #213
* Bug fix: Readme encoding error on some machines - fixes #214