Fix typo (fixes gh-1273)
Reverse priority of property sources when extracting sub properties

Fixes gh-1259
Documentation update

This commit fixes some inconsistent or outdated keys in the
documentation. More specifically:

* allowSessionOverride is no longer a template parameter
* templateEncoding has been renamed to charSet
* Groovy templates do not have the same configuration hierarchy, hence
  they don't share all settings
* spring.data.elasticsearch.local does not seem to exist
* flyway prefix and suffix should be sqlMigrationPrefix and suffix
* spring.rabbitmq.virtualHost had a typo
* endpoints.error.path is not a valid property
* shell.command-path-patterns had a typo
* spring.datasource.max-wait had a typo

Fixes gh-1226
Add java options for Heroku Procfile

Added $JAVA_OPTS variable to the sample Heroku Procfile.
If this is left out it can cause memory issues when the app starts.

Fixes gh-1266
Use class name not value to support non-Hibernate JPA vendors

With this change I got a simple Eclipselink version of the data-jpa
sample working. I'll push that when I get time to research it a bit more
(I needed to set up a Java agent so either that might be a problem
for our integration tests if we can't work around it).

Fixes gh-1268.