[File screen] change UI and fix bugs

[sonle-geekyants]

Is your feature request related to a problem? Please describe.

1. The download buttons are currently not working.
   https://github.com/atsign-foundation/atmosphere_pro/assets/88494375/7f81f753-ab41-4919-a7ef-920c4d361b25

2. The files that are not downloaded are allowed to open.
   

3. Fix the missing contact name leading to an error when changing the view type to List
   

Describe the solution you'd like

1. Remove the download buttons in the Files Screen
2. Add checkExist function to prevent opening files.
3. This issue happens to the Sent files when it is downloaded to the device, the contact name of them is returned null then leave it blank.

Describe alternatives you've considered

No response

Additional context

No response