Set more flexible naming scheme for template URLs, get from Controller

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/resources/templates/bookadd.html

@@ -9,7 +9,7 @@
 <div class="col-md-4 mb-3">
     <h1>Add new book</h1>
 
-    	<form th:object="${book}" action="#" th:action="@{bookadd}" method="post">
+    	<form th:object="${book}" action="#" th:action="@{__${addpage}__}" method="post">
 
     		<div class="form-group">
     			<label for="BookAuthor">Author</label>
@@ -62,7 +62,7 @@
     	</form>
 
     	<br>
-    	<form action="#" th:action="@{booklist}" method="get">
+    	<form action="#" th:action="@{__${listpage}__}" method="get">
     		<button class="btn btn-success" type="submit">Return to book list page</button>
     	</form>
 

bookstore/src/main/resources/templates/bookedit.html

@@ -62,7 +62,7 @@
     		<button class="btn btn-primary" type="submit">Update book</button>
     	</form>
     	<br>
-    	<form action="#" th:action="@{../booklist}" method="get">
+    	<form action="#" th:action="@{../__${listpage}__}" method="get">
     		<button class="btn btn-success" type="submit">Return to book list page</button>
     	</form>
 

bookstore/src/main/resources/templates/booklist.html

@@ -29,13 +29,13 @@
 				<td th:text="${#numbers.formatDecimal(book.price, 1, 2)}"></td>
 				<td><a class="btn btn-danger"
 				th:attr="onclick='javascript:return confirm(\'' + 'Delete book: ' + ${book.title} + '?' + '\');'"
-					th:href="@{bookdelete/{id}(id=${book.id})}">Delete</a></td>
+					th:href="@{__${deletepage}__/{id}(id=${book.id})}">Delete</a></td>
 				<td><a class="btn btn-warning"
-					th:href="@{bookedit/{id}(id=${book.id})}">Edit</a></td>
+					th:href="@{__${editpage}__/{id}(id=${book.id})}">Edit</a></td>
 			</tr>
 		</table>
 		<div>
-			<a class="btn btn-success" href="bookadd">Add Book</a>
+			<a class="btn btn-success" href="@{__${addpage}__}">Add Book</a>
 		</div>
 	</div>
 </body>