Add support for Conv1D on OpenCV backend
* Add support for Conv1D on OpenCV backend
* disable tests on other targets/backends
* Fix formatting
* Restore comment
* Remove unnecessary flag and fix test logic
* Fix perf test
* fix braces
* Fix indentation, assert check and remove unnecessary condition
* Remove unnecessary changes
* Add test cases for variable weights and bias
* dnn(conv): fallback on OpenCV+CPU instead of failures
* coding style
Sergei Slashchinin