AddConstantToPrimitive: fix package

For now, it should be imagej.ops.generated. In the future it would be
nice to generate ops into multiple packages which make sense for what
the op does. But for the time being the code generator always uses this
package.
Fix AddConstantToPrimitive template

There is no AddConstantToPrimitiveType superclass anymore...
generate.groovy: leverage groovyisms

We can use the nice script syntax of embedding variables in
double-quoted strings, instead of concatenating them with plus.
generate.groovy: detect & translate all templates
AddConstantToPrimitive: use distinct priorities
Use distinct priorities for "add" ops

There are some lurking issues with the number of overloaded add ops, and
how we match them in various circumstances. For now, we use different
priorities, carefully selected, to paper over the problem...
Add parallel version of DoubleType ArrayImg adder

At some point we will switch over to code generating these, but not yet.
Add an op for creating new images
DefaultASCII: fix bugs