ScreenManager retains reference to a removed method

[renonick87]

Bug Report

The SoftButtonManager refactor didn't change all references of update. Calling ScreenManagerBase.commit() results in a crash in the library. ScreenManagerBase's commit method needs to remove the call to this._softButtonManager.update().

Reproduction Steps

1. Call ScreenManagerBase.commit();

Expected Behavior

Any screen updates that have been made through the manager since beginTransaction was last called will be updated in the HMI.

Observed Behavior

The library crashes with the error message _softButtonManager.update is not a function error.

[renonick87]

Closed by #462