Add Possibility to change Server, Port, Username and Password and switch to Public Key auth

[Mannshoch]

Pre-Submission checklist

• There is no existing issue that already asks for this feature.
  
• The feature already exists in rclone (on your PC or in Termux)
• I am prepared to help make this feature

What version of RCX are you using (About -> App version)?

1.12.2 (22.07.2021)

What problem are you trying to solve?

Changing Server and Password

What should RCX be able to do differently to help with this problem?

1. Allow to edit a Remote
2. Allow change Server, Port, Username and Password
3. Add an Automatism to try to register a public key certificate so no username and password is required for connection.
   1. Create a new key-pair per Remote. Use the remote Password to encrypt the key-pair
   2. Try to ssh-copy-id to the server
   3. If successful use it that way. If not, remove the key pair and us username and password like before
   4. If Password is changed, change the password also on the key pair
   5. If a remote should be deleted, try to remove also the ID on server and remove the key pair also.
4. Check if username and password work and give feedback if not.