G-API: add transformation logic to GCompiler

* Introduce transformation logic to GCOmpiler

* Remove partialOk() method

* Fix minor issues

* Refactor code according to code review

1. Re-design matchPatternToSubstitute logic
2. Update transformations order
3. Replace check_transformations pass with a
   one time check in GCompiler ctor

* Revert unused nodes handling in pattern matching

* Address minor code review issues

* Address code review comments:

1) Fix some mistakes
2) Add new tests for endless loops
3) Update GCompiler's transformations logic

* Simplify GCompiler check for endless loops

1. Simplify transformations endless loops check:
 - Original idea wasn't a full solution
 - Need to develop a good method (heuristic?) to find loops
   in general case (TODO)
2. Remove irrelevant Endless Loops tests
3. Add new "bad arg" tests and unit tests

* Update comments