Add encryption category

[offa]

closes #446

[offa]

/cc @shuvashish76

[shuvashish76]

Remove duplicates.

• Cryptomator from File Sharing
• DroidFS from System
• Koofr Vault - I don't know how it works never tried it. I guess it's kinda trustworthy as available on official F-Droid repo.
• Valv already in Privacy & Security. It's specific to gallery vault not sure if it's necessary to move to this general category. As I mentioned in that issue, there are lot of apps related to encryption but for specific use cases.
• EDS Lite: Yes lets remove it. Especially as we've better alternative both client and encryption. It's the only foss option that support Veracrypt but at the same time see the problem with using this .

I'd suggest to change this category name to "File Encryption" i.e. intended to encrypt any type of files in general.

[offa]

Thanks for your comments, I have updated the PR accordingly.