This fixes the issue when bookmark search is started with 's' or 'j'.
Previously these letters were accelerators coming from the Go global menu,
which prevented from searching bookmarks started from the letters.
Now, the bookmark menu has a dedicated actions without the accelerators.
NOTE: The feature development is in progress. **All accepted reviews will be applied only to the bookmark-quicksearch branch**, so please accept if a patch solves the corresponding problem. For the branch merge to master I will send another code review where we can verify that every issue is addressed accordingly. I will also try to summarize the issues found in previous CRs.