Additional OAuth2 providers (#1010)

* add google+

* sort signin oauth2 providers based on the name so order is always the same

* update auth tip for google+

* add gitlab provider

* add bitbucket provider (and some go fmt)

* add twitter provider

* add facebook provider

* add dropbox provider

* add openid connect provider incl. new format of tips section in "Add New Source"

* lower the amount of disk storage for each session to prevent issues while building cross platform (and disk overflow)

* imports according to goimport and code style

* make it possible to set custom urls to gitlab and github provider (only these could have a different host)

* split up oauth2 into multiple files

* small typo in comment

* fix indention

* fix indentation

* fix new line before external import

* fix layout of signin part

* update "broken" dependency

templates/user/auth/link_account.tmpl

@@ -8,6 +8,8 @@
 		</div>
 	</div>
 </div>
+<div class="ui user signin container icon">
 {{template "user/auth/signin_inner" .}}
+</div>
 {{template "user/auth/signup_inner" .}}
 {{template "base/footer" .}}

templates/user/auth/signin_inner.tmpl

@@ -38,11 +38,14 @@
 				</div>
 			{{end}}
 
-			{{if .OAuth2Providers}}
+			{{if and .OrderedOAuth2Names .OAuth2Providers}}
 			<div class="ui attached segment">
 				<div class="oauth2 center">
 					<div>
-						<p>{{.i18n.Tr "sign_in_with"}}</p>{{range $key, $value := .OAuth2Providers}}<a href="{{AppSubUrl}}/user/oauth2/{{$key}}"><img alt="{{$value.DisplayName}}" title="{{$value.DisplayName}}" src="{{AppSubUrl}}{{$value.Image}}"></a>{{end}}
+						<p>{{.i18n.Tr "sign_in_with"}}</p>{{range $key := .OrderedOAuth2Names}}
+						{{$provider := index $.OAuth2Providers $key}}
+						<a href="{{AppSubUrl}}/user/oauth2/{{$key}}"><img alt="{{$provider.DisplayName}}{{if eq $provider.Name "openidConnect"}} ({{$key}}){{end}}" title="{{$provider.DisplayName}}{{if eq $provider.Name "openidConnect"}} ({{$key}}){{end}}" class="{{$provider.Name}}" src="{{AppSubUrl}}{{$provider.Image}}"></a>
+						{{end}}
 					</div>
 				</div>
 			</div>