Make mixin for fields in settings that need to be the same width

and make that width narrower so we can fit a tooltip in the left
hand side (they were a little too wide anyway for the kind of data
being entered, even on a narrow window).

res/css/views/settings/_ProfileSettings.scss

@@ -30,6 +30,10 @@ limitations under the License.
     margin-top: 0;
 }
 
+.mx_ProfileSettings_controls .mx_Field {
+    margin-right: 100px;
+}
+
 .mx_ProfileSettings_hostingSignup {
     margin-left: 20px;