Don't use form in ServerAdmin

Instead use raw ModelAdmin. It helps if there is need to
manually change is_measured flag.
Measure also cached memory in default memory sensors.

Previous version was giving extremely high "used memory"
measures.
use reverse resolver to determine skwissh LOGIN_URL

Still patching django.conf.settings but now it is possible to
place skwissh anywhere - not only under r'^skwissh/'.
Merge pull request #15 from swistakm/master

Thanks for your help...
Added jenkins support for home continuous integration.
pylint : unused import thread
pylint : unused import ServerForm
pep8 E121
pep8 corrections.
pep8 : blank line at the end of file
pep8 : blank line at the end of file
Added admin tests
Added test with Django1.5
Update .travis.yml