GH-525 cache constants and GH-526 query optimizer (#527)

* GH-526 add test

* improve how query explanation is transmitted and displayed to the user and move from node-sass to sass

* GH-525 cache getNobjects and capacity

* GH-526 update VariableToIdSubstitution to optimize at the StatementPattern level

qendpoint-core/src/main/java/com/the_qa_company/qendpoint/core/dictionary/impl/MultipleLangBaseDictionary.java

@@ -119,11 +119,19 @@ public long getNpredicates() {
 		return predicates.getNumberOfElements();
 	}
 
+	long cachedNobjects = -1;
+
 	@Override
 	public long getNobjects() {
-		return getNshared() + nonTyped.getNumberOfElements()
+		if (cachedNobjects != -1) {
+			return cachedNobjects;
+		}
+
+		long l = getNshared() + nonTyped.getNumberOfElements()
 				+ languages.values().stream().mapToLong(DictionarySection::getNumberOfElements).sum()
 				+ typed.values().stream().mapToLong(DictionarySection::getNumberOfElements).sum();
+		cachedNobjects = l;
+		return l;
 	}
 
 	@Override

qendpoint-core/src/main/java/com/the_qa_company/qendpoint/core/util/io/BigMappedByteBuffer.java

@@ -76,8 +76,17 @@ public void order(ByteOrder order) {
 	/**
 	 * @return the capacity of the big buffer
 	 */
+
+	long capacity = -1;
+
 	public long capacity() {
-		return buffers.stream().mapToLong(CloseMappedByteBuffer::capacity).sum();
+		if (capacity != -1) {
+			return capacity;
+		}
+
+		long sum = buffers.stream().mapToLong(CloseMappedByteBuffer::capacity).sum();
+		capacity = sum;
+		return sum;
 	}
 
 	private int getBufferOffset(long index) {