fix(custom-timelines): lookup profile by url

Closes #107. Instead of using the (wrong) profileID on CustomTimelines, use the URL, which will be correctly resolved.

mastodon/src/main/java/org/joinmastodon/android/ui/text/HtmlParser.java

@@ -100,7 +100,7 @@ public class HtmlParser{
 			}
 		}
 
-		Map<String, String> idsByUrl=mentions.stream().collect(Collectors.toMap(m->m.url, m->m.id));
+		Map<String, String> idsByUrl=mentions.stream().filter(mention -> mention.id != null).collect(Collectors.toMap(m->m.url, m->m.id));
 		// Hashtags in remote posts have remote URLs, these have local URLs so they don't match.
 //		Map<String, String> tagsByUrl=tags.stream().collect(Collectors.toMap(t->t.url, t->t.name));