cherry-pick all AsgTools updates from 21.2 into master

Mostly I was interested in getting !20396 (merged) into master, but the sweep failed as master is woefully behind 21.2 for AsgTools updates, so I now did a cherry-pick of all updates we made since July 2017 (when @akraszna did the last big update of the package in the master).

Now this is a fairly substantial update to a fairly central package. We'll have to do this (or something like it) eventually, but we may want to apply some caution when merging this in.

Complete list of commits cherry-picked:

• d9072d1a handle EventLoop algorithms correctly as tool parents
• f4ecf492 fix setting float properties from string
• fbc70ffc fix unit test for ANA_CHECK
• fb34aec0 fix unit tests
• b270a550 change the way AnaToolHandle creates tools
• bc25f631 remove unneeded local variable
• eba4b7df switch to linking either gtest or gmock
• 43f85b93 change ut_MessageCheck to use gtest
• 3141bb8c Merge branch 'asg_tool_creation' into '21.2'
• 3d44ae24 add a command line utility to check that tools can be created
• cbb734fd change the regular expression for tool names
• 62b5af99 support reading/writing enum properties via strings
• 35d084a0 improve type casting for setting tool properties
• 3e218c20 change how OutputLevel property gets registered
• 490ca69c Numerous improvements to how different analysis algs work
• 81f972d2 Fix standalone dictionary compilation
• c6db83cc create AsgTesting package from AsgTools package
• 807af8dc cmake dependency fix for Athena
• 6bcd5bf2 add AsgTools label to all of our unit tests