Add PHP Version Selector

[philipnewcomer]

Now that Pilothouse supports multiple PHP versions, it would be great to have a second toggle for this in addition to Xdebug. (I'm assuming a Chrome extension can create multiple icons?)

In this case, since it's not a boolean value we are changing, clicking on the icon should probably present a dropdown list of the available PHP versions.

It'd be great if the icon could have an overlay showing the current PHP version, like the Xdebug icon changes colors depending on whether it's on or off.

[Jaace]

There is an option to open a small HTML window below the icon - I'll take a look when I can - exciting news regarding the multiple PHP versions!

[Jaace]

It doesn't look like a single extension can produce two separate icons. It looks like we have a couple choices to make prior to moving forward with this feature:

1. Roll this into the same extension as XDebug, rename it, and instead of a binary action, we always show a dropdown with PHP version and an XDebug on/off choice for each. This would require six separate icons (or links) to click.

2. Keep this extension as XDebug only and create another extension to handle PHP version switching separately.
   Optionally, keep both of these extension directories in the same repo.

After thinking about this I think I prefer the keeping this functionality in two distinct Chrome Extensions; want to know your thoughts on this and about the repo setup.

[philipnewcomer]

I've found that only requiring a single click to toggle Xdebug has been very handy, so I don't think I'd want the Xdebug toggle to be hidden in submenu. Thus, let's create a separate extension for the PHP toggle and leave the Xdebug toggle as-is.

For now, let's keep both in the same repo, but we can split them out to separate repos in the future if this becomes unwieldy.

I'm going to rename this repo to pilothouse-chrome-extensions (plural), since there's now going to be multiple extensions here.