Add a gradle `ResolutionStrategy` that resolves missing version numbers
using the `spring-boot-dependencies` POM.

This commit also introduces a new `spring-boot-dependency-tools` module
that provides programmatic access to the `dependencyManagement` section
of the dependencies POM.

Fixed gh-262

--verbose seems to be only for CLI logging (so really only
for dependency resolution). --debug is interpreted by SpringApplication
but up to now has been extracted and deleted from the command line
by the CommandRunner. This change makes --debug set a System property
*and* pass it down to the application (if used with -- separator).

Fixes gh-266

Fixes gh-264

Fixes gh-260

spring.config.[name,location] can both be a comma-separated list now. Highest
priority is last, like a hash overriding its keys (as per other conventions
in the listener).

Fixes gh-261

If any @Import (or @Enable*, especially @EnableScheduling) has registered
bean *names* as ApplicationListeners, and the application context wasn't
refreshed fully when it failed, then the listener lookup could fail and
mask the original exception

Fixes gh-253

* Ensure prefix ends with period
* Allow prefix and key index to be set separately

Fixes gh-250

Declared spring-aspects as additional dependency in Spring Data JPA
starter pom. This is necessary to let the auditing feature work
correctly.

YAML documents can be text literals, so some common typos can be misleading
and not generate the expected exception (Boot fails to cast the
document to a Map, rather than reporting the underlying exception).

Fixes gh-235

Fixes gh-246

This reverts commit 3d60696b.

Fixes fg-243

Upgrade to Tomcat 7.0.50, working around the potential
NullPointerException by also adding dependencies to
tomcat-embedded-jasper (which is now also required for Hibernate
Validator 5.0, see commit 377953ba)

Fixes gh-245

Update Hibernate Validator dependency to 5.0.2 and also include
Tomcat Jasper dependency. Jasper is required as it provides the
default ExpressionFactory implementation class
(org.apache.el.ExpressionFactoryImpl) which is indirectly
instantiated by Hibernate Validator.

Fixes gh-173

Fixes gh-126