Add support for HTML injection

[QWp6t]

Resolves #1816

[oxyc]

In the case you're editing a file that causes a refresh and you save the file multiple times, there's the possibility that you get an outdated version if the browser is in the middle of a refresh when the save is detected.

I ran into this and used reloadDebounce instead. Seems pointless to trigger multiple refreshes in a row anyways.

[QWp6t]

The delay is an arbitrary one set by my plugin to invoke a delay between local file system updates and injection/reload by BrowserSync. This is to resolve an issue with BrowserSync reloading before the server (i.e., VM) has synchronized with local file changes. My plugin by default has this value set to 50ms, but it's 500ms in Sage because I'm assuming that most developers are using a VM.

Anyway, I could add a separate option for debounce as well, or possibly refactor my current implementation to use debounce instead. I'll look into it and do some tests.

[QWp6t]

@oxyc I added a debounce option to the plugin so you can set debounce in webpack.config.watch.js if you want, and it will get passed as the value to reloadDebounce. I might wind up implementing my own debounce as well to handle the different ways of resolving file update events.