scm refactor

- support multiple repositories
- module should be set per each file
- no admin part to administer
- improved svn hook
- workflow handleSCMCheckins module param is always null, workflow method may set $usr_id
simplify use NULL instead of NONE as string
restore previous workflow behaviour

if need to setup usr id, should add new workflow method with "pre" in it's name
Merge pull request #15 from glensc/scm-rewrite3

SCM rewrite