Pick icons on login screen by connector type instead of ID

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>

web/static/main.css

@@ -68,12 +68,12 @@ body {
   background-size: contain;
 }
 
-.dex-btn-icon--bitbucket {
+.dex-btn-icon--bitbucket-cloud {
   background-color: #205081;
   background-image: url(../static/img/bitbucket-icon.svg);
 }
 
-.dex-btn-icon--ldap, .dex-btn-icon--tectonic-ldap {
+.dex-btn-icon--ldap {
   background-color: #84B6EF;
   background-image: url(../static/img/ldap-icon.svg);
 }