feat(writekit): rename @robonen/editor to @robonen/writekit

Rename the rich-text editor package and all Editor* exports to Writekit*;
remove the old vue/editor tree.

vue/writekit/src/state/index.ts

@@ -0,0 +1,6 @@
+export * from './command';
+export * from './writekit-state';
+export * from './step';
+export * from './transaction';
+export * from './history';
+export * from './writekit';