fix dai::initialize() thread/except safety

[diablodale]

fixes #276 by using Meyer singleton + lambda.

This passed all 60/61 of the depthai-core test suite. The one test fails due to my OAK-D not having RGBD cali data in EEPROM.

[ctest] 
[ctest] 98% tests passed, 1 tests failed out of 61
[ctest] 
[ctest] Total Test time (real) = 1279.47 sec
[ctest] 
[ctest] The following tests FAILED:
[ctest] 	 51 - rgb_depth_aligned (Failed)
[ctest] Errors while running CTest
[ctest] CTest finished with return code 8

[Luxonis-Brandon]

Thanks for all the help. We can walk you through how to re-calibrate your OAK-D to get RGB calibration into it and we're also more than happy to just send you an additional OAK-D to say (1) thanks for all the help and (2) sorry yours was one of the very few that didn't get RGB calibration baked in (only some super-tiny number didn't get RGB cal).

If you'd like to do so feel free to shoot us an email at support at luxonis dot com.

[themarpe]

Thanks!