Auto-updatable version ranges

This commit improves the version format so that the minor and patch
elements can hold a special 'x' character besides the version, i.e.
`1.x.x.RELEASE` or `2.4.x.BUILD-SNAPSHOT`. A `VersionParser` now takes
care to resolve those against a list of known Spring Boot versions.

This is particularly useful in version ranges that have to change when
the latest Spring Boot versions change. Spring Initializr already auto-
udpates itself based on the sagan metadata. When a range is using this
feature, it is also automatically updated.

It might be hard to track the actual range values on a given instance so
an `InfoContributor` is now automatically exposed to list them.

Closes gh-328

initializr-web/src/main/groovy/io/spring/initializr/web/support/DefaultInitializrMetadataProvider.groovy

@@ -55,8 +55,7 @@ class DefaultInitializrMetadataProvider implements InitializrMetadataProvider {
 			if (!bootVersions.find { it.default }) { // No default specified
 				bootVersions[0].default = true
 			}
-			metadata.bootVersions.content.clear()
-			metadata.bootVersions.content.addAll(bootVersions)
+			metadata.updateSpringBootVersions(bootVersions)
 		}
 	}
 

initializr-web/src/main/groovy/io/spring/initializr/web/ui/UiController.groovy

@@ -22,7 +22,6 @@ import groovy.json.JsonBuilder
 import io.spring.initializr.metadata.Dependency
 import io.spring.initializr.metadata.InitializrMetadataProvider
 import io.spring.initializr.util.Version
-import io.spring.initializr.util.VersionRange
 
 import org.springframework.beans.factory.annotation.Autowired
 import org.springframework.http.MediaType
@@ -52,7 +51,7 @@ class UiController {
 		dependencyGroups.each { g ->
 			g.content.each { d ->
 				if (v && d.versionRange) {
-					if (VersionRange.parse(d.versionRange).match(v)) {
+					if (d.match(v)) {
 						content << new DependencyItem(g.name, d)
 					}
 				} else {