Add Setting for minimum refresh rate

[PaulBeasley]

By default it appears that this version (2,1,0-Beta.1) of sACNview has a refresh rate as low as 2 FPS. It appears some devices are interpreting that as a lost sACN source.

Please add a setting to manually set the minimum allowed refresh rate in a session.

[docsteer]

The sACN standard says

6.9.1 Network Data Loss Network data loss condition is a condition that is defined as either the absence of reception of E1.31 packets from a given source for a period of 2.5 seconds

So, those devices are definitely not complying with the standard. We can look at adding this feature as an advanced troubleshooting tool, but devices that fail to receive sACN from sACNView as it is right now do not comply to the standard and will likely have problems with other sACN sources as well..