generation and publishModel tasks.

PegasusPlugin:
 - With Gradle 3.0 and gradle daemon enabled, the plugin will not be
   loaded on every run. So the plugin cannot assume the static variables
   will be reset for each run. Fixed the issue by initializing these
   static variables in runOnce block.
CheckIdl, CheckRestModel and CheckSnapshot:
 - These tasks were ignoring the compat level flag while checking for
   status after the compat checker was run. Fix is to look at the result
of compat checker from the report it prints.
 - Add the compatibility report message to the global message to be
   printed out after build is finished.
 - Task was configured to fail only if both idl and models were
   incompatible. Fixed it to fail if either is incompatible.
 - Fixed the order of files in checkRestModel task (order was reversed
   earlier)

ChangedFileReport:
 - Changed the inputs to this task from generated files to source system
   files on which the report should be based on.
 - Now outputs list of files requiring checkin, which is printed after
   build is finished.