system groups - update system's list to include env and view

Adding a little more info to the system's list.
activation keys / systems - minor refactor to allow for reuse on system groups

For content views, we will be updating system groups to allow
the admin to change the env/view for all systems in a group.
This will use a similar env/view widget to what is currently
used in both activation keys and systems.  In preparation for
that, this commit is moving some of the logic to be common.

This commit primarily addresses:
1. moves the definition of 'no content view' - placing it in common_i18n
   and application_helper
2. moves the logic for obtaining the content view select labels
   to application_helper
ctivation keys / systems - mv i18n.update_view to _common_i18n partial

Renaming update_view to select_content_view and moving it to
the _common_i18n.html.haml partial.
activation keys - test fix
system groups - ui - allow user to change env/view for systems in a group

This commit contains changes to allow a user to navigate to
a system group and then 'edit' the environment/content view
for all systems in that group.

As part of the change, created env_content_view_selector.js, which
we may be able to leverage in other places in the UI where similar
behavior is used (e.g. activation key & system 'create').
system groups - address style comments from pull request 1837 review

Addresses a few minor style comments from 1837:
- spacing around => in controller
- spacing after lambda in controller
- inclusion of () on selector callback function
- indentation in *selector.js
Merge pull request #1837 from bbuckingham/fork-content_view_groups

system groups - UI - allow user to change the env/view for systems in a group