Box connection checks

Prevent connection of boxes if stream types are not compatible.

The IScenario class methods should already be managing this, and it probably just a matter of performing the right checks.

For info, the documentation on stream types: https://openvibe.inria.fr/stream-structures/ It should be possible to connect any input/output with the same stream type, and also inputs to outputs of a base type. See exemple (Signal type inherits from Streamed Matrix type):

Any other connection should fail and provide an error log message.