Added Additional Interceptors for Date Extraction

The Pattern Extractor Interceptor is used to extract strings that match regular expressions in headers or body of event
The extracted pattern can then be injected into a new header

The DateInterceptor is used to parse the time in a particular field and then inject it into the 'timestamp' field in the header

modified:   pom.xml
new file:   src/main/java/org/apache/flume/interceptor/DateInterceptor.java
new file:   src/main/java/org/apache/flume/interceptor/InterceptorStagingEnvironment.java
new file:   src/main/java/org/apache/flume/interceptor/PatternExtractorInterceptor.java