Bug 1059165 Part 1 - Always sync visibility for touch caret. r=ehsan

We should sync touch caret's visibility with caret every time since
touch caret might be hidden due to timeout while caret is enabled. Also
remove dead code.
Bug 1059165 Part 2 - Do not show touch caret when content is empty. r=ehsan
Bug 1059165 Part 3 - Add test_touchcaret_visibility.html. r=ehsan