Text Replacer example

[dotproto]

Adds a sample extension called "Text Replacer." As the name implies, this extension will replace a string in the page with a custom string. Currently supports 5 replacements.

This PR takes the place of #612, which I'm no longer able to directly update.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[patrickkettner]

Thanks a bunch, dude! couple of small things inline, and then

• the 19px image isn't used (probably remove it?). Also, could you add a 128px image, as thats the size the store requests folks add.
• Could you add a readme link the sibling functional samples?
• your google account is still attached to the commit, can you run git commit --amend --no-edit && git push --force-with-lease to clear it out so the CLA doesn't block?

[dotproto]

@patrickkettner, I think I've covered everything you request and all of the issues identified in #612.

[patrickkettner]

couple nits! License comment applies to all files that have BSD at the moment

[dotproto]

I suggest enabling Code review limits on this repo to prevent drive-by approvals.

[patrickkettner]

thanks!