mds: Interval tree implementation

mds: Interval tree implementation

Interval tree is an optimized data structure for representing and
querying intervals. Elementary intervals are represented as nodes of an
avl tree and the corresponding data is stored on these nodes based on a
concept of span. This representation allows log(n) (where n is the
number of data) storage. The balanced avl tree allows a log(n) query.
The implementation is a template class that is instantiated based on
parameters : - Interval type - Data type

Signed-off-by: Jojy George Varghese <jvarghese@scalecomputing.com>