reorganization of _examples and add some new examples such as iris+groupcache+mysql+docker

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/mvc/login-mvc-single-responsibility/views/user/login.html

@@ -0,0 +1,11 @@
+<form action="/user/login" method="POST">
+    <div class="container">
+        <label><b>Username</b></label>
+        <input type="text" placeholder="Enter Username" name="username" required>
+
+        <label><b>Password</b></label>
+        <input type="password" placeholder="Enter Password" name="password" required>
+
+        <button type="submit">Login</button>
+    </div>
+</form>

_examples/mvc/login-mvc-single-responsibility/views/user/me.html

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+<p>
+    Welcome back <strong>{{.User.Firstname}}</strong>!
+</p>

_examples/mvc/login-mvc-single-responsibility/views/user/notfound.html

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+<p>
+    User with ID <strong>{{.ID}}</strong> does not exist.
+</p>

_examples/mvc/login-mvc-single-responsibility/views/user/register.html

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+<form action="/user/register" method="POST">
+    <div class="container">
+        <label><b>Firstname</b></label>
+        <input type="text" placeholder="Enter Firstname" name="firstname" required>
+
+        <label><b>Username</b></label>
+        <input type="text" placeholder="Enter Username" name="username" required>
+
+        <label><b>Password</b></label>
+        <input type="password" placeholder="Enter Password" name="password" required>
+
+        <button type="submit">Register</button>
+    </div>
+</form>