Increased Test Coverage and Refactoring (EECE 310 L2A1)

Added new test cases to classes in crawljax-test-utils and crawljax-core:
* core/src/test/java/com/crawljax/core/TagAttributeTest.java
* core/src/test/java/com/crawljax/forms/FormInputTest.java
* core/src/test/java/com/crawljax/forms/InputValueTest.java
* core/src/test/java/com/crawljax/test/WebServerTest.java
* core/src/test/java/com/crawljax/util/DOMComparerTest.java
* core/src/test/java/com/crawljax/util/DomUtilsTest.java
* core/src/test/java/com/crawljax/util/HtmlNamespaceTest.java
* core/src/test/java/com/crawljax/util/UrlUtilsTest.java
* core/src/test/java/com/crawljax/util/XPathHelperTest.java
* test-utils/src/test/java/com/crawljax/crawljax_plugins_plugin/SampleCrawlersTest.java

Refactored based on violations in Sonar and code smells

Changed DomUtils' getTextValue method to properly execute compared to previous logic which never reached certain branches. 

Converted URL to URI before calling equals() or hashCode() to avoid potential blocking call or performance hit.