Update `Restarter` to support a `FailureHandler` strategy that can be
used to determine how to deal with errors. The
`LocalDevToolsAutoConfiguration` now uses a strategy that doesn't quit
the application, but instead continues to wait for further file changes.
This helps make restart much more usable in situations where you
accidentally break code.
Fixes gh-3210
Support loading a `.spring-boot-devtools.properties` file from the
users home folder. The property file can be used to customize settings
that make sense on a per-user basis, but might not want to be checked
into the project.
Fixes gh-3151
