qoraHoldersShare reworked to qoraHoldersShareByHeight.

This allows the QORA share percentage to be modified at different heights, based on community votes. Added unit test to simulate a reduction.

# Conflicts:
#	src/test/java/org/qortal/test/minting/RewardTests.java

src/main/resources/blockchain.json

@@ -46,7 +46,10 @@
 		{ "id": 4, "levels": [ 7, 8 ], "share": 0.20 },
 		{ "id": 5, "levels": [ 9, 10 ], "share": 0.25 }
 	],
-	"qoraHoldersShare": 0.20,
+	"qoraHoldersShareByHeight": [
+		{ "height": 1, "share": 0.20 },
+		{ "height": 9999999, "share": 0.01 }
+	],
 	"qoraPerQortReward": 250,
 	"minAccountsToActivateShareBin": 30,
 	"shareBinActivationMinLevel": 7,