In Shell-Mode: Use the connection as active context per default and add ability to switch contexts

[gitseti]

After connection in the shell mode the user should be act in the current context per default

Input
sh>con -h myHost.com -p 1884
Result

• client is connected and the prompt is working with that client as the active context:
  sh-ClientID@host>

The user should be able to switch between contextes and leave a context (without disconnect)
Input
sh-ClientID@host> switch_context -i 'other-id' -h 'other host'
sh-ClientID2@host2>

Input
sh-ClientID@host> leave_context
sh>

If working in a specific context

• the pub and sub command should not be extended from connect and use always the connection of the active context.
  (naming pub / sub should be the same )
• during active context another conn command should not possible