Make a IA.LimitedPrivate interface for CellComparator

CellCompartor has been added as an interface with IA.LimitedPrivate. It has the following methods #int compare(Cell leftCell, Cell rightCell); #int compareRows(Cell leftCell, Cell rightCell) #int compareRows(Cell cell, byte[] bytes, int offset, int length) #int compareWithoutRow(Cell leftCell, Cell rightCell) #int compareFamilies(Cell leftCell, Cell rightCell #int compareQualifiers(Cell leftCell, Cell rightCell) #int compareTimestamps(Cell leftCell, Cell rightCell) #int compareTimestamps(long leftCellts, long rightCellts) This is exposed to CPs and CPs can make use of the above methods to do comparisons on the cells. For internal usage we have CellComparatorImpl and it has static references to COMPARATOR and META_CELL_COMPARATOR. So when a region or store is initialized we should use one of the above comparator. For META table we need the META_CELL_COMPARATOR and all other table's regions/stores will use the COMPARTOR. While writing the comparator name in FixedFileTrailer of the Hfile we have now ensured that this rename of CellComparator.COMPARATOR/CellComparator.META_CELL_COMPARATOR to CellComparatorImpl.COMPARATOR/CellComparatorImpl.META_CELL_COMPARATOR is handled. CellUtils is an util method that provides lot of APIs that helps to do compare, matching functionalities between two cells, or with a cell and a corrpesponding byte[] etc. Some of the APIs are internally used which will be cleaned up in a follow on JIRA HBASE-18995 .