Make Ctrl+F not toggle the search mode but always enable it.

Switching back from other applications, the previous behavior of Ctrl+F
would often bother you in that it would dismiss the search widget if it
was already enabled when you meant by the key you wanted to perform a
search.

Making Ctrl+F always set you in search mode should save user from having
to care about the mode which is persistent across application switching
and database locking.
Complete remove the toggle search action.
Merge branch 'knu-untoggle_find'

https://github.com/keepassx/keepassx/pull/66