(GEOT-4963) Added fix for ContentFeatureStore.getCount() with startIndex...

Fix for ContentFeatureStore.getCount() with startIndex or MaxFeatures set (https://jira.codehaus.org/browse/GEOT-4963).
Modified test cases in ContentFeatureStore to test for getCount()
Added test cases to applicible extending classes. 
This import was throwing a compiler error in Eclipse for some reason. Tests still run fine using either Eclipse or mvn test