Code cleanup, factorization, and Java8 improvements.

src/qir/ast/expression/QIRReadVariable.java

src/qir/ast/value/QIRBaseValue.java

src/qir/ast/value/QIRBigNumber.java

src/qir/ast/value/QIRBoolean.java

src/qir/ast/value/QIRNumber.java

src/qir/ast/value/QIRString.java

src/qir/driver/QIROracleVisitor.java

src/qir/util/IQIRVisitor.java

src/qir/util/QIRPrintVisitor.java