* Adjusted fabric.Object so that chainable methods return superclass type instead of fabric.Object.
Also changed type of propertiesToInclude to string[] instead of any[]. Other methods related to props, such as `get()`, refer to properties as strings.
* Small tweaks to types
setBackgroundImage can omit callback
cornerStrokeColor is a property on object
rotateVector and qrDecompose are misc util functions
* Changed parameter types to be more precise. Used mapped types in get/set to enforce correct corresponding types
* Renamed non-existent classes and replaced with correct fabric classes
* Changed to pass linter
These weak type errors were not caught in TS 2.4 RC. The final TS 2.4
will catch weak type errors with primitives, so this PR fixes those
now-caught errors.
