Rewrite widgets with the new design and track down the progress

[Moppa5]

Description
As a part of the Up-To-Date project it was mentioned that we could convert Seravo Plugin widgets one by one to apply the new design. This issue is here just so that we can reference and keep track of the rewrite process.

Sitestatus

• Cache Status, contains "Toggle more" widget
• Site Information
• HTTP Request statistics
• Site checks, if possible ?
• Speed test
• Sanitize uploads
• Disk Usage
• Optimize Images
• Shadows

Upkeep

• Update Status
• Tests Status
• Changes Status
• Update tests
• Seravo Updates
• Screenshots ?
• Seravo Plugin Updater
• Change PHP Version

Database

• Database Access
• Manage the Database with Adminer
• Search-Replace Tool
• Database Cleanup Tool (optimize & cleanup)
• Database Size

Backups

• Backups, basic box
• Create a New Backup
• Files Excluded from the Backups
• Current Backups

Security

• Security (options)
• Last successful logins
• Check passwords
• Unnecessary themes
• Cruft Files
• Unnecessary plugins

Domains & Logs

• Domains & Mails bundled
• Logviewer ?

[JoosuaKoskinen]

I think it's currently possible to rewrite these:

• Site Status -> Site information
• Upkeep -> Update Status (probably)
• Upkeep -> Test Status
• Database -> Database Access
• Database -> Manage the Database with Adminer
• Backups -> Backups

After #549 these should be possible:

• Backups -> Files Excluded from the Backups
• Backups -> Current Backups
• Security -> Last successful logins

There will be a second AJAX handler and 'options/settings' upcoming very soon, I believe over 50% of postboxes can be rewritten then. And after possibility to add different kinds of graphs and tables I expect it to be at least 3/4 postboxes.

[Moppa5]

@JoosuaKoskinen, I can take a look at the following widgets next

• Site Information
• Test Status
• Last successful logins
• Update Status, marked as probably so need to investigate maybe?

Last successful logins probably needs the table helper as well so this could be taken care at the same time.