Add: synccron - Sync cron files from the central repository. Run from root's crontab.

This project was accepted in the LOPSA Mentorship Program 
(https://lopsa.org/mentor).

Overall design
--------------

1. Cron jobs are organized one file per server. Standard jobs
   applicable for a set of servers are in global files (for ERP,
   DB, web, etc.).

2. These files are under Subversion. The repository layout is as
   follows:

    . branches
    |--+ dev
    |  |--- hostname_00
    |  |--- ...
    |  |--- hostname_nn
    |  |--- web
    |  |--- erp
    |  |--- db
    |  |--- ...
    |--+ test ...
    |--+ prod ...

   (Global files should also fall under the respective 
   environments.)

3. An updated working copy is served via HTTP. The update to this
   working copy is done through hook scripts.

4. System administrators edit cron jobs per service or change 
   request and commit these to the repository.

5. Each server polls for changes (once daily) and retrieves the 
   latest update via `curl`. The file(s) are added to crontab. 
   Ad-hoc or on-demand changes can be done this way as well.