Implement storage for requests

[barryvdh]

This is the initial implementation of storage for the Debugbar. Uses the Magento filesystem to read/write files to the var folder. These files can be accessed through the API, using the browser button (3rd on the right of the toolbar).

Skips the collecting on internal routes, doesn't inject on ajax calls.

Possible future additions:

• Garbage collections (cleanup old files), could be done during cron?
• Database/Redis storage could be faster, but because it's development, not really needed.
• Data can be stacked, eg. for redirects and ajax calls. Not yet implemented here though.

[barryvdh]

I've now stacked redirect data and send the proper headers for XHR requests. Also generated the urls correctly and added a hash of the assets for the longer caching (in the previous PR).

I guess this is good to go now for me.

[elzekool]

Merged 😃

[barryvdh]

Thanks!