Support dual login via LDAP and forms authentication

Closes #256 as we now support dual login -- LDAP and forms authentication.

Also bumped the vendored library to LDAP.v3 as it contains bug fixes.

Gopkg.lock

@@ -299,12 +299,12 @@
   version = "v1.2"
 
 [[projects]]
-  digest = "1:93aaeb913621a3a53aaa78592c00f46d63e3bb0ea76e2d9b07327b50959a5778"
-  name = "gopkg.in/ldap.v2"
+  digest = "1:e9a0fa7c2dfc90e0fae16be5825ad98074d8704f5fcebfdc289a8e8fb0f8e4b5"
+  name = "gopkg.in/ldap.v3"
   packages = ["."]
   pruneopts = "UT"
-  revision = "bb7a9ca6e4fbc2129e3db588a34bc970ffe811a9"
-  version = "v2.5.1"
+  revision = "9f0d712775a0973b7824a1585a86a4ea1d5263d9"
+  version = "v3.0.3"
 
 [solve-meta]
   analyzer-name = "dep"
@@ -334,7 +334,7 @@
     "golang.org/x/oauth2",
     "gopkg.in/alexcesaro/quotedprintable.v3",
     "gopkg.in/andygrunwald/go-jira.v1",
-    "gopkg.in/ldap.v2",
+    "gopkg.in/ldap.v3",
   ]
   solver-name = "gps-cdcl"
   solver-version = 1