[intesis] Session Handling improved

[fd0cwp]

I have changed the login process so that the binding now only logs in at the beginning and logs out at the end of the lifetime. If a request fails due to a missing login or an invalid session ID, a new login attempt is made.

This ensures that

• Several requests can be sent in direct succession (if I switch the air conditioning from cooling to heating, I also want to change the slats at the same time)
• Less traffic is generated as there is not a constant logout and login again
• Ideally, the login credentials should only be visible once at startup

This change fixes openhab#15502.

Signed-off-by: Christoph fd0cwp@gmx.de