Consistent null, empty and blank String logic

[jonathanaustin]

WComponents uses a custom String helper class com.github.bordertech.wcomponents.util.Util to check and manipulate Strings.

This utility class has a method empty(String) which is misleading as it is testing if the String is blank (ie all whitespaces) instead of empty (ie length == 0). The use of the empty method through out WComponents needs to be reviewed to see if it is actually checking for null, empty or blank.

WComponents no longer needs to have a custom String library. Where possible the Util class should be replaced with the org.apache.commons.lang3.StringUtils.

The Util class should be deleted but as projects directly use it, it will need to be deprecated. However its internal logic can be replaced by making calls to StringUtils.