Improve file manager usability

[Smaug6739]

Few ideas to improve the usability of the CDN/file manager.

• On mobile drag and drop feature can't work, so we should improve the UI to facilitate uploads on mobile.
• We should also improve the UI of datatable bulk actions on mobile.
• Increase supported file types (all types of common documents should work)
• Detect unsupported file type from the frontend to improve experience (maybe disallow selection of unsupported files from the explorer)