Prevent sagan-common from having Spring 3.2.x on its classpath

Spring Social GitHub has a transitive dependency on spring-webmvc
3.2.x. In the absence of any other spring-webmvc dependency, this
causes a mixture of Spring 3.2.x and Spring 4.0.x to be on
sagan-common's classpath.

This commit adds an explicit dependency on spring-webmvc. No version
number is specified to allow the version to be determined by the
Spring Boot plugin.

An alternative approach would be to use a resolution strategy:

configurations.all {
    resolutionStrategy {
        eachDependency {
            if (it.details.requested.group == 'org.springframework') {
                details.useVersion '4.0.5.RELEASE'
            }
        }
    }
}

Unfortunately, this approach requires you to specify the version of
Spring that you want to use, thereby preventing you from automatically
using the version that's provided by the Spring Boot plugin. There's
an issue open (spring-projects/spring-boot#932) to make the versions
available as properties, but, until that functionality is available,
I think the change made in this commit is the best solution.
Merge pull request #409 from wilkinsona/consistent-spring-version

Prevent sagan-common from having Spring 3.2.x on its classpath
Upgrade to Boot 1.1

This commit updates Sagan to use Spring Boot 1.1.

Sagan's direct use of Flyway has been removed in favour of using the
Flyway auto-configuration that was added in Boot 1.1. To limit the
required configuration the migration scripts have been moved to their
default location.

namingstrategy has been renamed to naming_strategy. While
namingstrategy will work with Boot 1.1 it has been deprecated in
favor of naming_strategy. For consistent use of camel case ddl-auto
has been renamed ddl_auto.

Boot 1.1 now provides auto-configuration for Spring Social. With
spring-social-web on the classpath it will auto-configure a
ConnectController. While Sagan has spring-social-web on its classpath
it does not use a ConnectController, therefore the auto-configuration
has been explicitly excluded.