Enable thread safety checker for some trigger packages

Enable the thread safety checker for some of the MT-related trigger packages and fix a few small warnings found by it.

Trigger/TrigSteer/TrigOutputHandling is still to be done and is waiting for a fix to the gcc checker plugin.

This merge request affects 5 packages:

• Trigger/TrigSteer/DecisionHandling
• Trigger/TrigSteer/L1Decoder
• Trigger/TrigSteer/TrigHLTResultByteStream
• Trigger/TrigSteer/ViewAlgs
• Trigger/TrigSteer/ViewAlgsTest

added Trigger master review-pending-level-1 labels

CI Result SUCCESS

	Athena	AthSimulation
externals
cmake
make
required tests
optional tests

Full details available at NICOS MR-20956-2019-02-07-16-47
Athena: number of compilation errors 0, warnings 4
AthSimulation: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST 33477]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 81685468

added sweep:ignore label