Add the required keyword to some forms

This should improve a bit the accessibility.

airsonic-main/src/main/webapp/WEB-INF/jsp/login.jsp

@@ -21,9 +21,9 @@
 
             <div class="loginmessagetop"><sub:wiki text="${model.loginMessage}"/></div>
 
-            <input type="text" autofocus id="j_username" name="j_username" tabindex="1" placeholder="<fmt:message key="login.username"/>">
+            <input required type="text" autofocus id="j_username" name="j_username" tabindex="1" placeholder="<fmt:message key="login.username"/>">
 
-            <input type="password" autocomplete="off" name="j_password" tabindex="2" placeholder="<fmt:message key="login.password"/>">
+            <input required type="password" autocomplete="off"  name="j_password" tabindex="2" placeholder="<fmt:message key="login.password"/>">
 
             <input name="submit" type="submit" value="<fmt:message key="login.login"/>" tabindex="4"></td>
 

airsonic-main/src/main/webapp/WEB-INF/jsp/top.jsp

@@ -125,7 +125,7 @@
 
         <td style="padding-left:1em">
             <form method="post" action="search.view" target="main" name="searchForm">
-                <td><input type="text" name="query" id="query" size="28" placeholder="${search}" onclick="select();"
+                <td><input required type="text" name="query" id="query" size="28" placeholder="${search}" onclick="select();"
                            onkeyup="triggerInstantSearch();"></td>
                 <td><a href="javascript:document.searchForm.submit()"><img src="<spring:theme code="searchImage"/>" alt="${search}" title="${search}"></a></td>
             </form>