TextEditor: add methods 'typeAfter' and 'typeBefore'

In *org.jboss.reddeer.workbench.editor.TextEditor*

Add methods:
```java
/**
 * Method finds first occurrence of <i>word</i> and after that types <i>text</i>
 */
public void typeAfter(String word, String text)
```
```java
/**
 * Method finds first occurrence of <i>word</i> and before that types <i>text</i>
 */
public void typeBefore(String word, String text)
```