Nmap scan cleanup and enhancement

- Scan options can be manually entered or use pre-defined selection
- Nmap scan output added to task log
- Scan file output placed into data/scanfiles for regular storage, does
  not automatically delete
- HTML touchup
- Nmap command path can be defined in db.py
use os.getcwd() to set full path for _DATADIR_
group 50 services per schedule task for webshot

Rather than overload a single webshot process less split them into
groups of 50 and let the user run multiple scheduler services to handle
multiple processes.
fix ability to stop multiple tasks in the index

jQuery in tasks/index only picked up the first "#stop_button" for some
reason. Thus only the first button actually did anything. Changing this
to use $(".btn-danger") fixes it as long as we don't use more than 1
btn-danger on this page.
Tweaks to webimaging

- allow useragent to be set from args[3]
- default user agent includes "Kvasir"
- need to add ability in UI to select/enter a UA still
New vnc screenshot valkyrie and minor fixes

- VNC screenshot added. Requires the vncsnapshot binary. This can be
  installed in Ubuntu. For OSX you'll need to patch or use homebrew.

- Running valkyries grouped into a single fucntion in services.py
  controller. This will mean adding new ones may be fairly easy for
  running aginast services. Not sure about hosts, accounts, etc.

- Minor cleanup of log, shodanhq and db.py.sample