Use Common "Observation" Actions When Multiple Observers are Enabled

[kathlenemagnus-mips]

With the current Observer design, each Observer will define its own pre/post execute and pre exception Actions to be inserted into the Atlas flow. If multiple Observers are enabled, this could mean that several, redundant observation Actions are inserted, which will hurt the simulator's performance.

All Observers have a common purpose: collect information about Atlas's execution and write the output to some output format (database, log, CoSim Event, etc.). It should be pretty straightforward to define common "observation" Actions that can be used by all Observers that are enabled. This should reduce the code duplication and reduce the number of Actions needed to support multiple Observers.