Bug fixes
- Improved the building placer to use BWAPI->canBuildHere to verify that it case build besides that the area is free.
- Changed the behavior of build action to not fail when the worker is not going toward build position
- The retainer flushes the casebase after each goal get failed/succeeded.
- The retriever return similarity 0 for the goals parameters similarity if they are different.

Signed-off-by: Abdelrahman Elogeel <zikas_zak@hotmail.com>