Misc improvements to the web editor

1. When moving the mouse on the input of a block to create a new connection, the cursor mouse remains like a 'move item' cursor. It would be nice to have a different mouse cursor.

2. When creating a new connection by clicking on the input, it is not possible to cancel the creation of this connection. It should be possible by pressing 'esc'.

3. It is currently not possible to delete a 'wrong' connection.

4. For the analyzer, creating a simple toolchain, I was not able to change the synchronization channel.