fix freezing gui performance

[trittsv]

When there was a single topic with more then 200+ endpoints the gui was not useable, it was freezing to death. This PR fixes the performance issues, it now fully uses Signals/Slot (like qt suggest) and a performance fix in the qos check. The data handling is now more Object-Oriented, resulting in less looping to avoid unneeded cpu time.

• fix freezing gui - tested it with 600+ endpoints on a topic.
• fix performance hungry QoS mismatch check, compare only smallest needed subset.
• fix app crash when user copied something to clipboard.
• fix layout, last endpoint was only half visible.
• fix missing scroll bar in endpoint overview.
• fix gui-model update, use add/remove instead reset model every time.

@eboasson may you can have a look? 😃

[trittsv]

@eboasson thank you very much for you review and comments.

• I fixed the typo.
• Regarding the absence of mutex, its not needed anymore. Qts Signal/Slot mechanism with Qt::QueuedConnection is thread safe. Emitting the signal makes a copy and queues the data which then executed in the thread of the slot. The different threads now only communicate via signals/slot i removed all direct references.