PHOENIX-966 Context classloader for Phoenix classes

Temporarily set the current thread's context classloader in calls
that require creating an HBase configuration or accessing Phoenix
coprocessor endpoint classes.
PHOENIX-983 Add timezone offset function

Add a function to retrieve the GMT offset (in minutes) for a given
timezone and point in time.

Signed-off-by: Gabriel Reid <gabrielr@ngdata.com>
Changes from hortonworks phoenix-4.0.0.2.1.2.0
Renamed the mvn version to 4.0-tagged-etl
Added CHANGES notes on what we have done in this branch
Added ability to set the CurrentSCN during csv bulk loading
Using MYSQL format for csv bulk loader
Importing milliseconds with dates