editor-base: `command` now accepts functions as commands

Because the editor *needs* to have focus when executing a command, `focus()` is the very first thing called in `command`

Some commands however do not simply pass through to `_execCommand` (link being the primary use-case), so to avoid having to call `focus()` manually all over the codebase, passing a function into command seemed the best compromise.
editor-link: pass `_link` method to `command`
build gallery-sm-editor