BUG-1914: bump API requirement

This bumps the required maven API version 3.1.1 and removes the manual
override needed with previous versions.

Change-Id: If3b85169dccc9583ee93114c2b0c4f3fc9e17eb2
Signed-off-by: Robert Varga <rovarga@cisco.com>
BUG-2498: optimize enum's forValue() method

Use an ImmutableMap, as it provides optimized lookups based on
cardinality. Also hide the map from the package and turn it into a
constant.

Change-Id: I01591e56646705891fcc3fb8b871071169d35093
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-2498: optimize enum's forValue() method"
Merge "BUG-1914: bump API requirement"