accounts: add "extend from previous expiry"

If the expiry time of an expired user is still in the activity log,
extending and re-enabling a user with this option checked will extend
the expiry from this time, rather than the current time. For #379, i
think this is basically what they wanted.

css/tooltip.css

@@ -6,7 +6,7 @@
 .tooltip .content {
     visibility: hidden;
     opacity: 0;
-    max-width: 10rem;
+    max-width: 16rem;
     min-width: 6rem;
     background-color: rgba(0, 0, 0, 0.6);
     color: #fff;
@@ -29,6 +29,7 @@
 }
 
 .tooltip.above .content {
+    top: unset;
     bottom: calc(100% + 0.125rem);
     left: 50%;
     right: 0;