Introduce custom Exceptions

[marvin-we]

SQ and VSCode complain about using plain Exceptions - Any thoughts about this?

In case we want to fix it:

• Where to store them?
• Is there any hierarchy we want to create?

[marvin-we]

I have some things in mind where we can do different actions based on the Exception type. One concrete sample is the 'getClient' method of the 'ConnectionManager' - If we throw a dedicated Exception here, the 'CommunicationHandler' would be allowed to distinguish between:

• A general issue with the connection
• The fact that there is simply no client available