Add $prepare function to HalLink interface for templated URLs

Templated urls are of the form, e.g., `/api/v3/.../{user_id}`.
The HalLink had a flag that the given URL is templated, but no interface
to expand that link given a mapping for the templated parts.

This is required for the refactoring of the watchers tab.

frontend/app/components/api/api-v3/hal-link/hal-link.service.test.ts

@@ -229,5 +229,63 @@ describe('HalLink service', () => {
         runChecks();
       });
     });
+
+    describe('when $preparing the link', () => {
+      var func;
+
+      beforeEach(() => {
+        link.href = '/foo/bar/{user_id}';
+        link.title = 'title';
+        link.method = 'post';
+        link.templated = true;
+      });
+
+      describe('when the link is NOT templated', () => {
+        beforeEach(() => {
+          link.templated = false;
+        });
+        it('should raise an exception', () => {
+          expect(function() {
+            link.$prepare({});
+          }).to.throw;
+        });
+      });
+
+      describe('when the link is templated', () => {
+        beforeEach(() => {
+          func = link.$prepare({ user_id: '1234' });
+        });
+
+        it('should return a function that fetches the data', () => {
+          func();
+
+          $httpBackend.expectPOST('/foo/bar/1234').respond(200, {});
+          $httpBackend.flush();
+        });
+
+        it('should pass the params to $fetch', () => {
+          var $fetch = sinon.spy(func.$link, '$fetch');
+          func('hello');
+
+          expect($fetch.calledWith('hello')).to.be.true;
+        });
+
+        it('should have the untemplated href property', () => {
+          expect(func.href).to.equal('/foo/bar/1234');
+        });
+
+        it('should have the title property of the link', () => {
+          expect(func.title).to.equal(link.title);
+        });
+
+        it('should have the method property of the link', () => {
+          expect(func.method).to.equal(link.method);
+        });
+
+        it('should not be templated', () => {
+          expect(func.templated).to.equal(false);
+        });
+      });
+    });
   });
 });

frontend/app/components/api/api-v3/hal-link/hal-link.service.ts

@@ -76,6 +76,31 @@ export class HalLink implements HalLinkInterface {
     return halRequest.request(this.method, this.href, data, headers);
   }
 
+  /**
+   * Prepare the templated link and return a CallableHalLink with the templated parameters set
+   *
+   * @returns {CallableHalLink}
+   */
+  public $prepare(templateValues:{[templateKey:string]: string}) {
+    if (!this.templated) {
+      throw 'The link ' + this.href + ' is not templated.';
+    }
+
+    let href = _.clone(this.href);
+    _.each(templateValues, (value, key) => {
+      let regexp = new RegExp('{' + key + '}');
+      href = href.replace(regexp, value);
+    });
+
+    return HalLink.callable({
+      href: href,
+      title: this.title,
+      method: this.method,
+      templated: false,
+      payload: this.payload
+    });
+  }
+
   /**
    * Return a function that fetches the resource.
    *
@@ -95,6 +120,7 @@ export class HalLink implements HalLinkInterface {
 
     return linkFunc;
   }
+
 }
 
 function halLinkService(...args) {