Add a check to confirm plugin is available through dotorg

[maxinacube]

When triggering the extension, check if the plugins available for update are on dotorg

Some plugins allow updating through the WordPress Admin even though they are not available for direct download from the WordPress plugin repo. When gathering the slugs for the wpackagist composer list, we should loop through and hit https://api.wordpress.org/plugins/info/1.0/{slug}.json to check for a returned error before including it in the composer/packagist list.

[maxinacube]

@aaronware I pushed to the issue/5 branch

What I'm trying to do is reach out to the API in content.js and append a skipComposer true or false to the pluginData object based on the response.

From there, popup.js should look for the pluginData.skipComposer value to determine if the plugin should be included in the composer.json copy via the copyComposerPackages function

Another issue that I started seeing today - even after switching back to master to exclude my changes - is a JS error within the extension's popup.html

Unchecked runtime.lastError: The message port closed before a response was received.

Error handling response: TypeError: Cannot read property 'length' of undefined at chrome-extension://kknpefnigljpgndhdkicepfnhnnhcdhd/popup.js:44:64

popup.js line trigger the above error:
chrome.browserAction.setBadgeText({text: (response.length).toString(), tabId: tabs[0].id});