Re-order plugin entries by downloads count

Hi there.

As I see, currently Flow Launcher displays plugins in plugin store in the same order as they are present in plugins.json.
For small number of plugins it was fine, but right now when a lot of plugins have been created for Flow Launcher a lot of very useful and appreciated by users plugins may be at the end of the list in shadow of plugins created earlier.

My proposed quick and easy solution for this problem is to reorder plugins in plugin.json using downloads_count property exposed by GitHub API:
`https://api.github.com/repos/{repository_author}/{repository_name}/releases`.

Changes in the code will perform:
1. Send a request to the API
2. Iterate through records from API and sum downloads_count property
3. Order items by sum of downloads_count

As we know Flow Launcher is becoming a powerful tool thanks to it's strong community and plugins, this feature will result in much more pleasing user experience, especially for new users:
* New users will know right away which plugins are widely used and appreciated.
* Plugin store will be less cluttered with non-widely used plugins as they will be at the end of the list.
* Better UI experience as you do not have to scroll to the bottom of a large list to find something specific that is popular.