EECE310 teamL2C7: Fix for Issue#135 and Issue#151

Hi Alex,
For our EECE310 project, we fixed Issue#135 and Issue#151. We removed three files:
1) CrawlAttribute.java
2) TagAttribute.java
3) TagElement.java

We also removed some of the methods that uses TagAttribute class in CrawlElementExtractor.java as well, as it is no longer needed. 

When the user calls <code>click("div").withAttritbue("class", "redText")</code> or <code>click("div").withText("Text")</code>, Crawljax will convert it internally to XPath. Commands such as <code>click("div").withAttritbute("class", "redText").withAttribute("id", "idName")</code> or <code>click("div").withText("Text1").withText("Text2")</code> are also possible to allow users to select tags with different attributes/texts. Please let us know if you have any suggestions or concerns. 

Thanks!
Chris