Add support for dependency facet

This commit allows any dependency to be tagged with a facet. A facet
is a simple name that can be used to further tune the project request
if necessary.

Prior to this commit, the list of dependencies that were related to the
web was hardcoded. This was used for special handling such as adding
a dependency automatically if necessary of creating additional
resources in the project.

This logic was moved to a standard 'web' facet that any dependency
can declare through configuration.

Fixes gh-30

initializr-service/application.yml

@@ -42,6 +42,8 @@ initializr:
       content:
         - name: Web
           id: web
+          facets:
+            - web
         - name: Websocket
           id: websocket
         - name: Rest Repositories
@@ -52,12 +54,20 @@ initializr:
       content:
         - name: Freemarker
           id: freemarker
+          facets:
+            - web
         - name: Velocity
           id: velocity
+          facets:
+            - web
         - name: Groovy Templates
           id: groovy-templates
+          facets:
+            - web
         - name: Thymeleaf
           id: thymeleaf
+          facets:
+            - web
     - name: Social
       content:
         - name: Facebook