SyGuS streaming solution mode (#1131)

SyGuS streaming solution mode (#1131)

* Refactor conjecture class in ce guided instantiation, move to own file.  In preparation for sygus streaming mode.

* Infrastructure for streaming guards, more cleanup.

* Do explicit exclusion to move to next solution for sygus streaming option, now functional. More cleanup.

* More cleanup, add comments.

* Update comments

* Optimizations for invariant synthesis. Fix corner case for single invocation inference, more encapsulation in single inv utility. Minor fix for variable elimination in quantifiers rewriter.

* Fix makefile.

* Cleanup.

* Remove unused includes.

* Minor