Used implementation of the hasher includes salt itself, thus additional
salt is optional and can be safely (in terms of security) treat as empty
string
Note that this commit contains the following breaking changes:
* remote pull and remote push triggers are now enabled by default (with
empty target list)
* remote pull and remote push triggers now require target option to be
set (old behaviour had fallback on `gitremote`)
* validation is now considered to be stable, so it is enabled by default
in docker image (can be disabled however)
