Enhanced real-time synchronization block

[bernhard-thiele]

I'm working at an enhanced real-time synchronization block which has following enhancements compared to the present SynchronizeRealtime block:

• Supports simulations which start at initial times different to zero.
• Doesn't try to "catch-up" time if real-time dead-lines are missed (as the present SynchronizeRealtime block does). However, if this behavior is actually desired it is available as an optional catch-up mode.
• In addition to a non-sampled (continuous-time) mode, it optionally supports a sampled mode which is recommended for more deterministic, less solver sensitive behavior (but requires choosing appropriate sampling settings).
• Has improved diagnosis outputs which can help to understand real-time issues.
• Factors out the process priority settings in an independent block. Reason: In some applications real-time synchronization is achieved by waiting on an external signal, rather than the local real-time clock, but one still would like to increase the process priority.