Added checks for delegate methods and updated doc comments

[bummytime]

This PR:

• Updates invalid doc comments
• Adds checks for an optional delegate method to avoid crashes if not implemented: @selector(editorTrackStat:)
• Fixes an issue with addSlashes: method on WPEditorField.m and renames it to sanitizeHTML:

To test:

1. Build and run the Editor demo. Verify everything works and doc warnings are gone.
2. Build and run WPiOS on this branch. Verify everything works.

@elibud would you mind reviewing?

[diegoreymendez]

Unfortunately stripping Javascript from HTML may not be very trivial.

Here's an old personal attempt to solve a similar issue, that simply turned off an old post-creating mechanism in the App, instead of stripping JS code.

Sorry I didn't provide this information before but I only remembered about it now.

I'll check if our endpoint is actually taking care of stripping the JS code, since that would make this issue mostly cosmetic (ie: client-side only).

[bummytime]

ty @elibud and @diegoreymendez !