Polish
Allow prefixed bytes with fat JARs

Update `spring-boot-loader` ZIP processing code to support prefixed
bytes within the fat jar. This technique allows a bash script to be
embedded at the start of the JAR whilst still allowing `java -jar`
execution.

Fixes gh-1073
Improve error message on condition exceptions

Catch exceptions thrown from SpringBootCondition and re-throw with
more context.

See gh-1098