feat(expressions): Allowing to globally configure SPEL evaluator vers…

…ion (spinnaker#1592)

- Adding an option to configure the SPEL evaluator version
- Added missing copyright header to some classes

fix(core): handle incoming non-parallelized pipelines

fix(core): apply metric recording when reading executions from Redis

fix(canary): fix Orchestration constructor in DeployCanary stage (spi…

…nnaker#1585)

fix(persistence): requisiteStageRefIds can be null in Redis (spinnake…

…r#1584)

feat(pipeline_template): Partials-generated stages should be given ge…

…nerated group name (spinnaker#1574)

fix(pipeline_template): Plan serialization & empty string rendering (s…

…pinnaker#1581)

* fix(pipeline_template): Render empty strings as null

* fix(pipeline_template): Fix method signature now that spring pays attention

fix(expressions): allow unevaluated values in V2 evaluator (spinnaker…

…#1577)

- Fix a regression in v2 to not prematurely flag an expression as failed

chore(springBoot): Upgrade to Spring Boot 1.5.4 (spinnaker#1486)

fix(pipeline_templates): notification inheritance (spinnaker#1576)