Speedup and simplify tests

This drastically speeds up tests and simplifies test writing by making
it so that no explicit calls for waiting are needed. Elements that are
queried for now implicitly waits for them to be available.

On my machine, tests used to take 3-4 minutes to complete. Now they take
~1 minute to complete.

tests/browsertests/issue181.nim

@@ -5,8 +5,6 @@ import webdriver
 proc test*(session: Session, baseUrl: string) =
   session.navigate(baseUrl)
 
-  waitForLoad(session)
-
   test "can see banned posts":
     with session:
       register("issue181", "issue181")
@@ -19,7 +17,6 @@ proc test*(session: Session, baseUrl: string) =
 
       login("issue181", "issue181")
       navigate(baseUrl)
-      wait()
 
       const title = "Testing issue 181."
       createThread(title, "Test for issue #181")
@@ -33,7 +30,6 @@ proc test*(session: Session, baseUrl: string) =
 
       # Make sure the banned user's thread is still visible.
       navigate(baseUrl)
-      wait()
       ensureExists("tr.banned")
       checkText("tr.banned .thread-title > a", title)
       logout()